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 $93.30   11.822%   $104.3299   $104.33   $104.35   $104.30  
  Purchase #2 $179.92   12.593%   $202.5773   $202.58   $202.60   $202.60  
  Purchase #3 $204.70   7.825%   $220.7178   $220.72   $220.70   $220.70  
  Purchase #4 $244.80   9.228%   $267.3901   $267.39   $267.40   $267.40  
  Purchase #5 $5.76   8.451%   $6.2468   $6.25   $6.25   $6.20  
  Purchase #6 $92.42   5.102%   $97.1353   $97.14   $97.15   $97.10  
  Purchase #7 $132.29   13.600%   $150.2814   $150.28   $150.30   $150.30  
  7 purchase totals = $953.19       $1,048.6786   $1,048.69   $1,048.75   $1,048.60