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 $97.79   5.276%   $102.9494   $102.95   $102.95   $102.90  
  Purchase #2 $197.31   4.240%   $205.6759   $205.68   $205.70   $205.70  
  Purchase #3 $183.43   10.484%   $202.6608   $202.66   $202.65   $202.70  
  Purchase #4 $183.97   12.843%   $207.5973   $207.60   $207.60   $207.60  
  Purchase #5 $103.81   10.112%   $114.3073   $114.31   $114.30   $114.30  
  Purchase #6 $59.74   7.642%   $64.3053   $64.31   $64.30   $64.30  
  Purchase #7 $139.62   4.568%   $145.9978   $146.00   $146.00   $146.00  
  7 purchase totals = $965.67       $1,043.4938   $1,043.51   $1,043.50   $1,043.50