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 $61.35   13.602%   $69.6948   $69.69   $69.70   $69.70  
  Purchase #2 $36.75   9.488%   $40.2368   $40.24   $40.25   $40.20  
  Purchase #3 $177.43   13.657%   $201.6616   $201.66   $201.65   $201.70  
  Purchase #4 $85.62   9.207%   $93.503   $93.50   $93.50   $93.50  
  Purchase #5 $98.74   3.826%   $102.5178   $102.52   $102.50   $102.50  
  Purchase #6 $177.84   12.396%   $199.885   $199.89   $199.90   $199.90  
  Purchase #7 $88.57   12.252%   $99.4216   $99.42   $99.40   $99.40  
  7 purchase totals = $726.30       $806.9206   $806.92   $806.90   $806.90