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 $59.64   6.864%   $63.7337   $63.73   $63.75   $63.70  
  Purchase #2 $103.98   6.550%   $110.7907   $110.79   $110.80   $110.80  
  Purchase #3 $108.98   10.416%   $120.3314   $120.33   $120.35   $120.30  
  Purchase #4 $95.54   4.252%   $99.6024   $99.60   $99.60   $99.60  
  Purchase #5 $22.81   13.776%   $25.9523   $25.95   $25.95   $26.00  
  Purchase #6 $250.56   5.280%   $263.7896   $263.79   $263.80   $263.80  
  Purchase #7 $62.46   13.481%   $70.8802   $70.88   $70.90   $70.90  
  7 purchase totals = $703.97       $755.0803   $755.07   $755.15   $755.10