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 $56.50   12.520%   $63.5738   $63.57   $63.55   $63.60  
  Purchase #2 $180.31   7.437%   $193.7197   $193.72   $193.70   $193.70  
  Purchase #3 $22.56   11.633%   $25.1844   $25.18   $25.20   $25.20  
  Purchase #4 $91.72   7.541%   $98.6366   $98.64   $98.65   $98.60  
  Purchase #5 $113.35   13.776%   $128.9651   $128.97   $128.95   $129.00  
  Purchase #6 $71.51   13.468%   $81.141   $81.14   $81.15   $81.10  
  Purchase #7 $151.48   3.178%   $156.294   $156.29   $156.30   $156.30  
  7 purchase totals = $687.43       $747.5146   $747.51   $747.50   $747.50