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 $93.73   5.598%   $98.977   $98.98   $99.00   $99.00  
  Purchase #2 $225.54   5.779%   $238.574   $238.57   $238.55   $238.60  
  Purchase #3 $133.94   5.612%   $141.4567   $141.46   $141.45   $141.50  
  Purchase #4 $166.77   8.108%   $180.2917   $180.29   $180.30   $180.30  
  Purchase #5 $135.96   12.815%   $153.3833   $153.38   $153.40   $153.40  
  Purchase #6 $62.53   10.740%   $69.2457   $69.25   $69.25   $69.20  
  Purchase #7 $142.67   7.351%   $153.1577   $153.16   $153.15   $153.20  
  7 purchase totals = $961.14       $1,035.0861   $1,035.09   $1,035.10   $1,035.20