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 $126.41   6.612%   $134.7682   $134.77   $134.75   $134.80  
  Purchase #2 $182.67   7.432%   $196.246   $196.25   $196.25   $196.20  
  Purchase #3 $111.54   5.257%   $117.4037   $117.40   $117.40   $117.40  
  Purchase #4 $24.33   6.679%   $25.955   $25.96   $25.95   $26.00  
  Purchase #5 $38.65   8.222%   $41.8278   $41.83   $41.85   $41.80  
  Purchase #6 $210.87   10.497%   $233.005   $233.01   $233.00   $233.00  
  Purchase #7 $221.78   9.476%   $242.7959   $242.80   $242.80   $242.80  
  7 purchase totals = $916.25       $992.0016   $992.02   $992.00   $992.00