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 $189.95   10.342%   $209.5946   $209.59   $209.60   $209.60  
  Purchase #2 $118.34   9.388%   $129.4498   $129.45   $129.45   $129.40  
  Purchase #3 $90.74   4.261%   $94.6064   $94.61   $94.60   $94.60  
  Purchase #4 $237.99   11.821%   $266.1228   $266.12   $266.10   $266.10  
  Purchase #5 $81.42   7.567%   $87.5811   $87.58   $87.60   $87.60  
  Purchase #6 $119.93   10.541%   $132.5718   $132.57   $132.55   $132.60  
  Purchase #7 $153.78   13.443%   $174.4526   $174.45   $174.45   $174.50  
  7 purchase totals = $992.15       $1,094.3791   $1,094.37   $1,094.35   $1,094.40