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 $57.62   12.779%   $64.9833   $64.98   $65.00   $65.00  
  Purchase #2 $197.74   9.545%   $216.6143   $216.61   $216.60   $216.60  
  Purchase #3 $164.73   10.480%   $181.9937   $181.99   $182.00   $182.00  
  Purchase #4 $164.51   9.372%   $179.9279   $179.93   $179.95   $179.90  
  Purchase #5 $95.98   11.157%   $106.6885   $106.69   $106.70   $106.70  
  Purchase #6 $186.91   6.447%   $198.9601   $198.96   $198.95   $199.00  
  Purchase #7 $246.80   4.363%   $257.5679   $257.57   $257.55   $257.60  
  7 purchase totals = $1,114.29       $1,206.7357   $1,206.73   $1,206.75   $1,206.80