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 $194.70   6.739%   $207.8208   $207.82   $207.80   $207.80  
  Purchase #2 $183.38   11.647%   $204.7383   $204.74   $204.75   $204.70  
  Purchase #3 $244.37   13.277%   $276.815   $276.82   $276.80   $276.80  
  Purchase #4 $70.87   9.834%   $77.8394   $77.84   $77.85   $77.80  
  Purchase #5 $39.56   8.132%   $42.777   $42.78   $42.80   $42.80  
  Purchase #6 $227.73   11.796%   $254.593   $254.59   $254.60   $254.60  
  Purchase #7 $14.55   8.263%   $15.7523   $15.75   $15.75   $15.80  
  7 purchase totals = $975.16       $1,080.3358   $1,080.34   $1,080.35   $1,080.30