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 $95.84   6.424%   $101.9968   $102.00   $102.00   $102.00  
  Purchase #2 $61.47   12.182%   $68.9583   $68.96   $68.95   $69.00  
  Purchase #3 $223.64   3.336%   $231.1006   $231.10   $231.10   $231.10  
  Purchase #4 $80.83   8.463%   $87.6706   $87.67   $87.65   $87.70  
  Purchase #5 $190.67   5.388%   $200.9433   $200.94   $200.95   $200.90  
  Purchase #6 $67.38   3.130%   $69.489   $69.49   $69.50   $69.50  
  Purchase #7 $66.37   7.553%   $71.3829   $71.38   $71.40   $71.40  
  7 purchase totals = $786.20       $831.5415   $831.54   $831.55   $831.60