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 $68.86   6.347%   $73.2305   $73.23   $73.25   $73.20  
  Purchase #2 $128.93   4.572%   $134.8247   $134.82   $134.80   $134.80  
  Purchase #3 $172.92   11.507%   $192.8179   $192.82   $192.80   $192.80  
  Purchase #4 $170.94   12.603%   $192.4836   $192.48   $192.50   $192.50  
  Purchase #5 $148.29   4.526%   $155.0016   $155.00   $155.00   $155.00  
  Purchase #6 $224.95   8.488%   $244.0438   $244.04   $244.05   $244.00  
  Purchase #7 $70.61   6.193%   $74.9829   $74.98   $75.00   $75.00  
  7 purchase totals = $985.50       $1,067.3850   $1,067.37   $1,067.40   $1,067.30