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 $60.62   7.683%   $65.2774   $65.28   $65.30   $65.30  
  Purchase #2 $60.52   12.356%   $67.9979   $68.00   $68.00   $68.00  
  Purchase #3 $159.52   3.762%   $165.5211   $165.52   $165.50   $165.50  
  Purchase #4 $55.96   4.163%   $58.2896   $58.29   $58.30   $58.30  
  Purchase #5 $200.89   7.455%   $215.8663   $215.87   $215.85   $215.90  
  Purchase #6 $138.90   10.842%   $153.9595   $153.96   $153.95   $154.00  
  Purchase #7 $166.85   10.730%   $184.753   $184.75   $184.75   $184.80  
  7 purchase totals = $843.26       $911.6648   $911.67   $911.65   $911.80