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 $246.46   11.117%   $273.859   $273.86   $273.85   $273.90  
  Purchase #2 $38.69   7.235%   $41.4892   $41.49   $41.50   $41.50  
  Purchase #3 $97.97   11.760%   $109.4913   $109.49   $109.50   $109.50  
  Purchase #4 $166.78   7.450%   $179.2051   $179.21   $179.20   $179.20  
  Purchase #5 $249.79   3.417%   $258.3253   $258.33   $258.35   $258.30  
  Purchase #6 $155.71   3.620%   $161.3467   $161.35   $161.35   $161.30  
  Purchase #7 $31.55   7.833%   $34.0213   $34.02   $34.00   $34.00  
  7 purchase totals = $986.95       $1,057.7379   $1,057.75   $1,057.75   $1,057.70