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 $112.53   11.131%   $125.0557   $125.06   $125.05   $125.10  
  Purchase #2 $224.99   9.483%   $246.3258   $246.33   $246.35   $246.30  
  Purchase #3 $141.51   5.205%   $148.8756   $148.88   $148.90   $148.90  
  Purchase #4 $223.91   6.497%   $238.4574   $238.46   $238.45   $238.50  
  Purchase #5 $41.55   9.512%   $45.5022   $45.50   $45.50   $45.50  
  Purchase #6 $14.33   13.543%   $16.2707   $16.27   $16.25   $16.30  
  Purchase #7 $205.64   13.324%   $233.0395   $233.04   $233.05   $233.00  
  7 purchase totals = $964.46       $1,053.5269   $1,053.54   $1,053.55   $1,053.60