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 $228.94   7.874%   $246.9667   $246.97   $246.95   $247.00  
  Purchase #2 $235.68   6.381%   $250.7187   $250.72   $250.70   $250.70  
  Purchase #3 $189.31   6.163%   $200.9772   $200.98   $201.00   $201.00  
  Purchase #4 $193.33   5.300%   $203.5765   $203.58   $203.60   $203.60  
  Purchase #5 $246.73   11.597%   $275.3433   $275.34   $275.35   $275.30  
  Purchase #6 $111.40   4.254%   $116.139   $116.14   $116.15   $116.10  
  Purchase #7 $14.41   12.256%   $16.1761   $16.18   $16.20   $16.20  
  7 purchase totals = $1,219.80       $1,309.8975   $1,309.91   $1,309.95   $1,309.90