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 $44.80   11.510%   $49.9565   $49.96   $49.95   $50.00  
  Purchase #2 $227.94   12.582%   $256.6194   $256.62   $256.60   $256.60  
  Purchase #3 $176.73   9.761%   $193.9806   $193.98   $194.00   $194.00  
  Purchase #4 $217.82   9.292%   $238.0598   $238.06   $238.05   $238.10  
  Purchase #5 $122.88   11.343%   $136.8183   $136.82   $136.80   $136.80  
  Purchase #6 $98.95   11.104%   $109.9374   $109.94   $109.95   $109.90  
  Purchase #7 $67.37   3.417%   $69.672   $69.67   $69.65   $69.70  
  7 purchase totals = $956.49       $1,055.0440   $1,055.05   $1,055.00   $1,055.10