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 $48.71   3.791%   $50.5566   $50.56   $50.55   $50.60  
  Purchase #2 $161.74   12.377%   $181.7586   $181.76   $181.75   $181.80  
  Purchase #3 $133.92   7.239%   $143.6145   $143.61   $143.60   $143.60  
  Purchase #4 $185.30   11.207%   $206.0666   $206.07   $206.05   $206.10  
  Purchase #5 $248.40   7.786%   $267.7404   $267.74   $267.75   $267.70  
  Purchase #6 $133.68   7.793%   $144.0977   $144.10   $144.10   $144.10  
  Purchase #7 $178.63   12.174%   $200.3764   $200.38   $200.40   $200.40  
  7 purchase totals = $1,090.38       $1,194.2108   $1,194.22   $1,194.20   $1,194.30