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 $78.41   13.106%   $88.6864   $88.69   $88.70   $88.70  
  Purchase #2 $182.96   11.479%   $203.962   $203.96   $203.95   $204.00  
  Purchase #3 $90.58   4.578%   $94.7268   $94.73   $94.75   $94.70  
  Purchase #4 $56.54   11.797%   $63.21   $63.21   $63.20   $63.20  
  Purchase #5 $249.58   4.817%   $261.6023   $261.60   $261.60   $261.60  
  Purchase #6 $220.30   7.817%   $237.5209   $237.52   $237.50   $237.50  
  Purchase #7 $31.30   6.413%   $33.3073   $33.31   $33.30   $33.30  
  7 purchase totals = $909.67       $983.0157   $983.02   $983.00   $983.00