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 $126.35   6.563%   $134.6424   $134.64   $134.65   $134.60  
  Purchase #2 $45.55   12.686%   $51.3285   $51.33   $51.35   $51.30  
  Purchase #3 $50.38   5.303%   $53.0517   $53.05   $53.05   $53.10  
  Purchase #4 $245.25   11.153%   $272.6027   $272.60   $272.60   $272.60  
  Purchase #5 $126.31   6.601%   $134.6477   $134.65   $134.65   $134.60  
  Purchase #6 $194.90   5.342%   $205.3116   $205.31   $205.30   $205.30  
  Purchase #7 $173.72   6.232%   $184.5462   $184.55   $184.55   $184.50  
  7 purchase totals = $962.46       $1,036.1308   $1,036.13   $1,036.15   $1,036.00