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 $88.93   13.731%   $101.141   $101.14   $101.15   $101.10  
  Purchase #2 $184.56   5.398%   $194.5225   $194.52   $194.50   $194.50  
  Purchase #3 $118.46   8.374%   $128.3798   $128.38   $128.40   $128.40  
  Purchase #4 $19.66   3.587%   $20.3652   $20.37   $20.35   $20.40  
  Purchase #5 $113.76   5.398%   $119.9008   $119.90   $119.90   $119.90  
  Purchase #6 $165.40   5.684%   $174.8013   $174.80   $174.80   $174.80  
  Purchase #7 $24.66   13.714%   $28.0419   $28.04   $28.05   $28.00  
  7 purchase totals = $715.43       $767.1525   $767.15   $767.15   $767.10