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 $36.87   12.462%   $41.4647   $41.46   $41.45   $41.50  
  Purchase #2 $152.25   11.436%   $169.6613   $169.66   $169.65   $169.70  
  Purchase #3 $218.71   6.110%   $232.0732   $232.07   $232.05   $232.10  
  Purchase #4 $124.72   13.404%   $141.4375   $141.44   $141.45   $141.40  
  Purchase #5 $50.53   7.134%   $54.1348   $54.13   $54.15   $54.10  
  Purchase #6 $228.95   8.209%   $247.7445   $247.74   $247.75   $247.70  
  Purchase #7 $196.77   7.542%   $211.6104   $211.61   $211.60   $211.60  
  7 purchase totals = $1,008.80       $1,098.1264   $1,098.11   $1,098.10   $1,098.10