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 $244.86   12.528%   $275.5361   $275.54   $275.55   $275.50  
  Purchase #2 $206.95   11.606%   $230.9686   $230.97   $230.95   $231.00  
  Purchase #3 $91.33   8.490%   $99.0839   $99.08   $99.10   $99.10  
  Purchase #4 $241.61   8.338%   $261.7554   $261.76   $261.75   $261.80  
  Purchase #5 $35.51   6.592%   $37.8508   $37.85   $37.85   $37.90  
  Purchase #6 $248.39   4.175%   $258.7603   $258.76   $258.75   $258.80  
  Purchase #7 $16.40   7.594%   $17.6454   $17.65   $17.65   $17.60  
  7 purchase totals = $1,085.05       $1,181.6005   $1,181.61   $1,181.60   $1,181.70