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 $227.73   3.332%   $235.318   $235.32   $235.30   $235.30  
  Purchase #2 $52.70   12.265%   $59.1637   $59.16   $59.15   $59.20  
  Purchase #3 $30.73   11.714%   $34.3297   $34.33   $34.35   $34.30  
  Purchase #4 $228.32   3.227%   $235.6879   $235.69   $235.70   $235.70  
  Purchase #5 $28.81   13.139%   $32.5953   $32.60   $32.60   $32.60  
  Purchase #6 $162.53   8.541%   $176.4117   $176.41   $176.40   $176.40  
  Purchase #7 $230.48   5.703%   $243.6243   $243.62   $243.60   $243.60  
  7 purchase totals = $961.30       $1,017.1306   $1,017.13   $1,017.10   $1,017.10