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 $55.67   13.556%   $63.2166   $63.22   $63.20   $63.20  
  Purchase #2 $137.53   10.417%   $151.8565   $151.86   $151.85   $151.90  
  Purchase #3 $184.98   9.524%   $202.5975   $202.60   $202.60   $202.60  
  Purchase #4 $13.73   4.797%   $14.3886   $14.39   $14.40   $14.40  
  Purchase #5 $245.41   9.233%   $268.0687   $268.07   $268.05   $268.10  
  Purchase #6 $25.65   11.715%   $28.6549   $28.65   $28.65   $28.70  
  Purchase #7 $212.40   8.660%   $230.7938   $230.79   $230.80   $230.80  
  7 purchase totals = $875.37       $959.5766   $959.58   $959.55   $959.70