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 $118.61   13.180%   $134.2428   $134.24   $134.25   $134.20  
  Purchase #2 $191.86   11.310%   $213.5594   $213.56   $213.55   $213.60  
  Purchase #3 $66.67   13.678%   $75.7891   $75.79   $75.80   $75.80  
  Purchase #4 $203.90   3.547%   $211.1323   $211.13   $211.15   $211.10  
  Purchase #5 $195.59   6.143%   $207.6051   $207.61   $207.60   $207.60  
  Purchase #6 $61.53   5.390%   $64.8465   $64.85   $64.85   $64.80  
  Purchase #7 $123.73   4.475%   $129.2669   $129.27   $129.25   $129.30  
  7 purchase totals = $961.89       $1,036.4421   $1,036.45   $1,036.45   $1,036.40