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 $228.38   3.663%   $236.7456   $236.75   $236.75   $236.70  
  Purchase #2 $162.27   11.663%   $181.1956   $181.20   $181.20   $181.20  
  Purchase #3 $42.62   7.610%   $45.8634   $45.86   $45.85   $45.90  
  Purchase #4 $51.43   11.868%   $57.5337   $57.53   $57.55   $57.50  
  Purchase #5 $60.56   13.873%   $68.9615   $68.96   $68.95   $69.00  
  Purchase #6 $113.30   4.201%   $118.0597   $118.06   $118.05   $118.10  
  Purchase #7 $235.29   7.628%   $253.2379   $253.24   $253.25   $253.20  
  7 purchase totals = $893.85       $961.5974   $961.60   $961.60   $961.60