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 $85.44   3.276%   $88.239   $88.24   $88.25   $88.20  
  Purchase #2 $95.71   8.372%   $103.7228   $103.72   $103.70   $103.70  
  Purchase #3 $74.28   5.383%   $78.2785   $78.28   $78.30   $78.30  
  Purchase #4 $207.70   5.756%   $219.6552   $219.66   $219.65   $219.70  
  Purchase #5 $232.77   11.127%   $258.6703   $258.67   $258.65   $258.70  
  Purchase #6 $131.47   12.461%   $147.8525   $147.85   $147.85   $147.90  
  Purchase #7 $43.91   6.847%   $46.9165   $46.92   $46.90   $46.90  
  7 purchase totals = $871.28       $943.3348   $943.34   $943.30   $943.40