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 $61.46   12.232%   $68.9778   $68.98   $69.00   $69.00  
  Purchase #2 $89.50   4.849%   $93.8399   $93.84   $93.85   $93.80  
  Purchase #3 $224.70   8.859%   $244.6062   $244.61   $244.60   $244.60  
  Purchase #4 $176.95   13.263%   $200.4189   $200.42   $200.40   $200.40  
  Purchase #5 $66.75   4.628%   $69.8392   $69.84   $69.85   $69.80  
  Purchase #6 $135.86   11.872%   $151.9893   $151.99   $152.00   $152.00  
  Purchase #7 $171.78   8.601%   $186.5548   $186.55   $186.55   $186.60  
  7 purchase totals = $927.00       $1,016.2261   $1,016.23   $1,016.25   $1,016.20