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 $238.40   11.420%   $265.6253   $265.63   $265.65   $265.60  
  Purchase #2 $205.35   9.695%   $225.2587   $225.26   $225.25   $225.30  
  Purchase #3 $8.78   9.718%   $9.6332   $9.63   $9.65   $9.60  
  Purchase #4 $98.71   3.277%   $101.9447   $101.94   $101.95   $101.90  
  Purchase #5 $155.31   13.437%   $176.179   $176.18   $176.20   $176.20  
  Purchase #6 $92.84   7.359%   $99.6721   $99.67   $99.65   $99.70  
  Purchase #7 $200.29   6.589%   $213.4871   $213.49   $213.50   $213.50  
  7 purchase totals = $999.68       $1,091.8001   $1,091.80   $1,091.85   $1,091.80