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 $226.49   3.653%   $234.7637   $234.76   $234.75   $234.80  
  Purchase #2 $181.89   13.312%   $206.1032   $206.10   $206.10   $206.10  
  Purchase #3 $204.65   6.163%   $217.2626   $217.26   $217.25   $217.30  
  Purchase #4 $129.73   6.844%   $138.6087   $138.61   $138.60   $138.60  
  Purchase #5 $216.40   5.504%   $228.3107   $228.31   $228.30   $228.30  
  Purchase #6 $22.72   11.278%   $25.2824   $25.28   $25.30   $25.30  
  Purchase #7 $224.98   8.142%   $243.2979   $243.30   $243.30   $243.30  
  7 purchase totals = $1,206.86       $1,293.6292   $1,293.62   $1,293.60   $1,293.70