Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.43   5.471%   $262.0216   $262.02   $262.00   $262.00  
  Purchase #2 $137.35   9.762%   $150.7581   $150.76   $150.75   $150.80  
  Purchase #3 $145.70   13.205%   $164.9397   $164.94   $164.95   $164.90  
  Purchase #4 $223.97   6.556%   $238.6535   $238.65   $238.65   $238.70  
  Purchase #5 $148.86   8.219%   $161.0948   $161.09   $161.10   $161.10  
  Purchase #6 $192.86   12.107%   $216.2096   $216.21   $216.20   $216.20  
  Purchase #7 $152.79   12.368%   $171.6871   $171.69   $171.70   $171.70  
  7 purchase totals = $1,249.96       $1,365.3644   $1,365.36   $1,365.35   $1,365.40