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 $178.43   10.408%   $197.001   $197.00   $197.00   $197.00  
  Purchase #2 $83.82   3.474%   $86.7319   $86.73   $86.75   $86.70  
  Purchase #3 $111.61   6.145%   $118.4684   $118.47   $118.45   $118.50  
  Purchase #4 $122.89   13.328%   $139.2688   $139.27   $139.25   $139.30  
  Purchase #5 $57.45   13.482%   $65.1954   $65.20   $65.20   $65.20  
  Purchase #6 $212.50   6.872%   $227.103   $227.10   $227.10   $227.10  
  Purchase #7 $246.36   10.817%   $273.0088   $273.01   $273.00   $273.00  
  7 purchase totals = $1,013.06       $1,106.7773   $1,106.78   $1,106.75   $1,106.80