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 $245.72   12.472%   $276.3662   $276.37   $276.35   $276.40  
  Purchase #2 $45.56   13.684%   $51.7944   $51.79   $51.80   $51.80  
  Purchase #3 $218.58   9.609%   $239.5834   $239.58   $239.60   $239.60  
  Purchase #4 $97.44   8.220%   $105.4496   $105.45   $105.45   $105.40  
  Purchase #5 $226.67   10.282%   $249.9762   $249.98   $250.00   $250.00  
  Purchase #6 $213.42   7.403%   $229.2195   $229.22   $229.20   $229.20  
  Purchase #7 $161.51   12.194%   $181.2045   $181.20   $181.20   $181.20  
  7 purchase totals = $1,208.90       $1,333.5938   $1,333.59   $1,333.60   $1,333.60