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 $246.77   5.775%   $261.021   $261.02   $261.00   $261.00  
  Purchase #2 $235.45   9.812%   $258.5524   $258.55   $258.55   $258.60  
  Purchase #3 $65.98   12.354%   $74.1312   $74.13   $74.15   $74.10  
  Purchase #4 $150.76   10.244%   $166.2039   $166.20   $166.20   $166.20  
  Purchase #5 $117.48   13.286%   $133.0884   $133.09   $133.10   $133.10  
  Purchase #6 $141.81   5.458%   $149.55   $149.55   $149.55   $149.60  
  Purchase #7 $71.32   4.667%   $74.6485   $74.65   $74.65   $74.60  
  7 purchase totals = $1,029.57       $1,117.1954   $1,117.19   $1,117.20   $1,117.20