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 $238.61   11.317%   $265.6135   $265.61   $265.60   $265.60  
  Purchase #2 $23.38   11.803%   $26.1395   $26.14   $26.15   $26.10  
  Purchase #3 $118.37   4.236%   $123.3842   $123.38   $123.40   $123.40  
  Purchase #4 $179.87   13.262%   $203.7244   $203.72   $203.70   $203.70  
  Purchase #5 $30.67   3.345%   $31.6959   $31.70   $31.70   $31.70  
  Purchase #6 $137.98   5.870%   $146.0794   $146.08   $146.10   $146.10  
  Purchase #7 $222.99   11.681%   $249.0375   $249.04   $249.05   $249.00  
  7 purchase totals = $951.87       $1,045.6744   $1,045.67   $1,045.70   $1,045.60