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 $195.74   3.694%   $202.9706   $202.97   $202.95   $203.00  
  Purchase #2 $103.55   3.554%   $107.2302   $107.23   $107.25   $107.20  
  Purchase #3 $118.56   5.409%   $124.9729   $124.97   $124.95   $125.00  
  Purchase #4 $88.65   11.432%   $98.7845   $98.78   $98.80   $98.80  
  Purchase #5 $102.44   3.476%   $106.0008   $106.00   $106.00   $106.00  
  Purchase #6 $232.88   7.115%   $249.4494   $249.45   $249.45   $249.40  
  Purchase #7 $156.41   7.342%   $167.8936   $167.89   $167.90   $167.90  
  7 purchase totals = $998.23       $1,057.3020   $1,057.29   $1,057.30   $1,057.30