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 $54.87   8.237%   $59.3896   $59.39   $59.40   $59.40  
  Purchase #2 $232.29   8.305%   $251.5817   $251.58   $251.60   $251.60  
  Purchase #3 $195.88   12.464%   $220.2945   $220.29   $220.30   $220.30  
  Purchase #4 $27.39   6.662%   $29.2147   $29.21   $29.20   $29.20  
  Purchase #5 $244.62   9.477%   $267.8026   $267.80   $267.80   $267.80  
  Purchase #6 $53.75   8.627%   $58.387   $58.39   $58.40   $58.40  
  Purchase #7 $132.28   4.465%   $138.1863   $138.19   $138.20   $138.20  
  7 purchase totals = $941.08       $1,024.8564   $1,024.85   $1,024.90   $1,024.90