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 $227.48   11.457%   $253.5424   $253.54   $253.55   $253.50  
  Purchase #2 $91.93   11.640%   $102.6307   $102.63   $102.65   $102.60  
  Purchase #3 $185.30   5.387%   $195.2821   $195.28   $195.30   $195.30  
  Purchase #4 $95.35   11.511%   $106.3257   $106.33   $106.35   $106.30  
  Purchase #5 $192.73   13.761%   $219.2516   $219.25   $219.25   $219.30  
  Purchase #6 $173.88   7.804%   $187.4496   $187.45   $187.45   $187.40  
  Purchase #7 $13.61   6.492%   $14.4936   $14.49   $14.50   $14.50  
  7 purchase totals = $980.28       $1,078.9757   $1,078.97   $1,079.05   $1,078.90