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 $141.59   11.735%   $158.2056   $158.21   $158.20   $158.20  
  Purchase #2 $226.71   3.626%   $234.9305   $234.93   $234.95   $234.90  
  Purchase #3 $187.75   9.823%   $206.1927   $206.19   $206.20   $206.20  
  Purchase #4 $58.57   7.372%   $62.8878   $62.89   $62.90   $62.90  
  Purchase #5 $242.86   3.163%   $250.5417   $250.54   $250.55   $250.50  
  Purchase #6 $195.65   3.701%   $202.891   $202.89   $202.90   $202.90  
  Purchase #7 $171.65   6.845%   $183.3994   $183.40   $183.40   $183.40  
  7 purchase totals = $1,224.78       $1,299.0487   $1,299.05   $1,299.10   $1,299.00