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 $231.93   11.213%   $257.9363   $257.94   $257.95   $257.90  
  Purchase #2 $141.91   9.371%   $155.2084   $155.21   $155.20   $155.20  
  Purchase #3 $82.83   13.471%   $93.988   $93.99   $94.00   $94.00  
  Purchase #4 $58.62   9.240%   $64.0365   $64.04   $64.05   $64.00  
  Purchase #5 $16.36   8.651%   $17.7753   $17.78   $17.80   $17.80  
  Purchase #6 $213.81   8.369%   $231.7038   $231.70   $231.70   $231.70  
  Purchase #7 $199.83   10.505%   $220.8221   $220.82   $220.80   $220.80  
  7 purchase totals = $945.29       $1,041.4704   $1,041.48   $1,041.50   $1,041.40