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 $26.51   3.232%   $27.3668   $27.37   $27.35   $27.40  
  Purchase #2 $152.50   10.830%   $169.0158   $169.02   $169.00   $169.00  
  Purchase #3 $50.62   7.360%   $54.3456   $54.35   $54.35   $54.30  
  Purchase #4 $55.91   5.530%   $59.0018   $59.00   $59.00   $59.00  
  Purchase #5 $73.57   4.484%   $76.8689   $76.87   $76.85   $76.90  
  Purchase #6 $210.68   7.559%   $226.6053   $226.61   $226.60   $226.60  
  Purchase #7 $58.52   10.840%   $64.8636   $64.86   $64.85   $64.90  
  7 purchase totals = $628.31       $678.0678   $678.08   $678.00   $678.10