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 $134.44   11.397%   $149.7621   $149.76   $149.75   $149.80  
  Purchase #2 $182.46   7.689%   $196.4893   $196.49   $196.50   $196.50  
  Purchase #3 $81.82   7.289%   $87.7839   $87.78   $87.80   $87.80  
  Purchase #4 $149.36   7.417%   $160.438   $160.44   $160.45   $160.40  
  Purchase #5 $178.67   11.728%   $199.6244   $199.62   $199.60   $199.60  
  Purchase #6 $90.54   6.869%   $96.7592   $96.76   $96.75   $96.80  
  Purchase #7 $118.98   10.788%   $131.8156   $131.82   $131.80   $131.80  
  7 purchase totals = $936.27       $1,022.6725   $1,022.67   $1,022.65   $1,022.70