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 $90.97   3.602%   $94.2467   $94.25   $94.25   $94.20  
  Purchase #2 $117.41   11.828%   $131.2973   $131.30   $131.30   $131.30  
  Purchase #3 $68.38   8.817%   $74.4091   $74.41   $74.40   $74.40  
  Purchase #4 $118.49   6.387%   $126.058   $126.06   $126.05   $126.10  
  Purchase #5 $186.67   13.744%   $212.3259   $212.33   $212.35   $212.30  
  Purchase #6 $117.62   5.142%   $123.668   $123.67   $123.65   $123.70  
  Purchase #7 $184.36   8.258%   $199.5844   $199.58   $199.60   $199.60  
  7 purchase totals = $883.90       $961.5894   $961.60   $961.60   $961.60