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 $238.82   12.774%   $269.3269   $269.33   $269.35   $269.30  
  Purchase #2 $103.88   8.148%   $112.3441   $112.34   $112.35   $112.30  
  Purchase #3 $221.33   13.239%   $250.6319   $250.63   $250.65   $250.60  
  Purchase #4 $155.51   3.413%   $160.8176   $160.82   $160.80   $160.80  
  Purchase #5 $74.79   3.746%   $77.5916   $77.59   $77.60   $77.60  
  Purchase #6 $190.59   12.434%   $214.288   $214.29   $214.30   $214.30  
  Purchase #7 $159.35   13.385%   $180.679   $180.68   $180.70   $180.70  
  7 purchase totals = $1,144.27       $1,265.6791   $1,265.68   $1,265.75   $1,265.60