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 $55.79   10.207%   $61.4845   $61.48   $61.50   $61.50  
  Purchase #2 $44.88   5.507%   $47.3515   $47.35   $47.35   $47.40  
  Purchase #3 $189.98   4.177%   $197.9155   $197.92   $197.90   $197.90  
  Purchase #4 $192.81   6.685%   $205.6993   $205.70   $205.70   $205.70  
  Purchase #5 $52.98   3.760%   $54.972   $54.97   $54.95   $55.00  
  Purchase #6 $139.28   4.708%   $145.8373   $145.84   $145.85   $145.80  
  Purchase #7 $46.98   3.582%   $48.6628   $48.66   $48.65   $48.70  
  7 purchase totals = $722.70       $761.9229   $761.92   $761.90   $762.00