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 $247.88   11.225%   $275.7045   $275.70   $275.70   $275.70  
  Purchase #2 $23.30   8.165%   $25.2024   $25.20   $25.20   $25.20  
  Purchase #3 $59.60   8.565%   $64.7047   $64.70   $64.70   $64.70  
  Purchase #4 $21.71   7.849%   $23.414   $23.41   $23.40   $23.40  
  Purchase #5 $247.69   12.675%   $279.0847   $279.08   $279.10   $279.10  
  Purchase #6 $185.90   8.720%   $202.1105   $202.11   $202.10   $202.10  
  Purchase #7 $149.72   10.172%   $164.9495   $164.95   $164.95   $164.90  
  7 purchase totals = $935.80       $1,035.1703   $1,035.15   $1,035.15   $1,035.10