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 $49.71   9.813%   $54.588   $54.59   $54.60   $54.60  
  Purchase #2 $85.99   13.578%   $97.6657   $97.67   $97.65   $97.70  
  Purchase #3 $242.37   3.485%   $250.8166   $250.82   $250.80   $250.80  
  Purchase #4 $23.67   12.735%   $26.6844   $26.68   $26.70   $26.70  
  Purchase #5 $195.28   12.116%   $218.9401   $218.94   $218.95   $218.90  
  Purchase #6 $188.36   9.159%   $205.6119   $205.61   $205.60   $205.60  
  Purchase #7 $143.81   3.739%   $149.1871   $149.19   $149.20   $149.20  
  7 purchase totals = $929.19       $1,003.4938   $1,003.50   $1,003.50   $1,003.50