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 $203.66   6.282%   $216.4539   $216.45   $216.45   $216.50  
  Purchase #2 $186.28   7.373%   $200.0144   $200.01   $200.00   $200.00  
  Purchase #3 $174.56   13.143%   $197.5024   $197.50   $197.50   $197.50  
  Purchase #4 $91.50   11.826%   $102.3208   $102.32   $102.30   $102.30  
  Purchase #5 $24.76   10.761%   $27.4244   $27.42   $27.40   $27.40  
  Purchase #6 $244.51   3.556%   $253.2048   $253.20   $253.20   $253.20  
  Purchase #7 $69.87   4.499%   $73.0135   $73.01   $73.00   $73.00  
  7 purchase totals = $995.14       $1,069.9342   $1,069.91   $1,069.85   $1,069.90