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 $114.74   9.191%   $125.2858   $125.29   $125.30   $125.30  
  Purchase #2 $59.87   4.179%   $62.372   $62.37   $62.35   $62.40  
  Purchase #3 $121.45   11.135%   $134.9735   $134.97   $134.95   $135.00  
  Purchase #4 $205.45   4.553%   $214.8041   $214.80   $214.80   $214.80  
  Purchase #5 $77.53   12.246%   $87.0243   $87.02   $87.00   $87.00  
  Purchase #6 $245.50   6.517%   $261.4992   $261.50   $261.50   $261.50  
  Purchase #7 $144.83   7.472%   $155.6517   $155.65   $155.65   $155.70  
  7 purchase totals = $969.37       $1,041.6106   $1,041.60   $1,041.55   $1,041.70