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 $187.33   8.576%   $203.3954   $203.40   $203.40   $203.40  
  Purchase #2 $54.77   9.556%   $60.0038   $60.00   $60.00   $60.00  
  Purchase #3 $162.53   7.454%   $174.645   $174.65   $174.65   $174.60  
  Purchase #4 $217.38   8.874%   $236.6703   $236.67   $236.65   $236.70  
  Purchase #5 $184.25   7.149%   $197.422   $197.42   $197.40   $197.40  
  Purchase #6 $125.26   13.471%   $142.1338   $142.13   $142.15   $142.10  
  Purchase #7 $83.66   11.510%   $93.2893   $93.29   $93.30   $93.30  
  7 purchase totals = $1,015.18       $1,107.5596   $1,107.56   $1,107.55   $1,107.50