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 $236.84   13.652%   $269.1734   $269.17   $269.15   $269.20  
  Purchase #2 $222.82   12.580%   $250.8508   $250.85   $250.85   $250.90  
  Purchase #3 $159.73   5.678%   $168.7995   $168.80   $168.80   $168.80  
  Purchase #4 $171.67   11.504%   $191.4189   $191.42   $191.40   $191.40  
  Purchase #5 $227.55   3.532%   $235.5871   $235.59   $235.60   $235.60  
  Purchase #6 $70.86   5.593%   $74.8232   $74.82   $74.80   $74.80  
  Purchase #7 $166.62   10.362%   $183.8852   $183.89   $183.90   $183.90  
  7 purchase totals = $1,256.09       $1,374.5381   $1,374.54   $1,374.50   $1,374.60