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 $48.97   12.404%   $55.0442   $55.04   $55.05   $55.00  
  Purchase #2 $168.87   3.237%   $174.3363   $174.34   $174.35   $174.30  
  Purchase #3 $194.28   8.827%   $211.4291   $211.43   $211.45   $211.40  
  Purchase #4 $113.44   9.588%   $124.3166   $124.32   $124.30   $124.30  
  Purchase #5 $237.60   7.796%   $256.1233   $256.12   $256.10   $256.10  
  Purchase #6 $157.55   5.222%   $165.7773   $165.78   $165.80   $165.80  
  Purchase #7 $244.52   12.102%   $274.1118   $274.11   $274.10   $274.10  
  7 purchase totals = $1,165.23       $1,261.1386   $1,261.14   $1,261.15   $1,261.00