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 $187.58   8.584%   $203.6819   $203.68   $203.70   $203.70  
  Purchase #2 $187.48   9.603%   $205.4837   $205.48   $205.50   $205.50  
  Purchase #3 $173.65   7.269%   $186.2726   $186.27   $186.25   $186.30  
  Purchase #4 $52.38   3.790%   $54.3652   $54.37   $54.35   $54.40  
  Purchase #5 $30.63   8.104%   $33.1123   $33.11   $33.10   $33.10  
  Purchase #6 $231.56   10.117%   $254.9869   $254.99   $255.00   $255.00  
  Purchase #7 $115.43   9.480%   $126.3728   $126.37   $126.35   $126.40  
  7 purchase totals = $978.71       $1,064.2754   $1,064.27   $1,064.25   $1,064.40