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 $47.93   3.681%   $49.6943   $49.69   $49.70   $49.70  
  Purchase #2 $181.83   7.123%   $194.7818   $194.78   $194.80   $194.80  
  Purchase #3 $212.33   7.240%   $227.7027   $227.70   $227.70   $227.70  
  Purchase #4 $162.71   11.427%   $181.3029   $181.30   $181.30   $181.30  
  Purchase #5 $229.75   6.390%   $244.431   $244.43   $244.45   $244.40  
  Purchase #6 $202.69   13.474%   $230.0005   $230.00   $230.00   $230.00  
  Purchase #7 $201.47   6.679%   $214.9262   $214.93   $214.95   $214.90  
  7 purchase totals = $1,238.71       $1,342.8394   $1,342.83   $1,342.90   $1,342.80