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 $228.86   7.845%   $246.8141   $246.81   $246.80   $246.80  
  Purchase #2 $236.72   13.383%   $268.4002   $268.40   $268.40   $268.40  
  Purchase #3 $25.52   13.804%   $29.0428   $29.04   $29.05   $29.00  
  Purchase #4 $75.85   8.639%   $82.4027   $82.40   $82.40   $82.40  
  Purchase #5 $185.54   9.138%   $202.4946   $202.49   $202.50   $202.50  
  Purchase #6 $129.85   11.228%   $144.4296   $144.43   $144.45   $144.40  
  Purchase #7 $183.81   6.814%   $196.3348   $196.33   $196.35   $196.30  
  7 purchase totals = $1,066.15       $1,169.9188   $1,169.90   $1,169.95   $1,169.80