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 $64.70   5.365%   $68.1712   $68.17   $68.15   $68.20  
  Purchase #2 $244.60   13.777%   $278.2985   $278.30   $278.30   $278.30  
  Purchase #3 $132.35   9.865%   $145.4063   $145.41   $145.40   $145.40  
  Purchase #4 $67.90   11.566%   $75.7533   $75.75   $75.75   $75.80  
  Purchase #5 $68.67   9.507%   $75.1985   $75.20   $75.20   $75.20  
  Purchase #6 $233.56   9.163%   $254.9611   $254.96   $254.95   $255.00  
  Purchase #7 $61.40   11.360%   $68.375   $68.38   $68.40   $68.40  
  7 purchase totals = $873.18       $966.1639   $966.17   $966.15   $966.30