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 $72.41   6.784%   $77.3223   $77.32   $77.30   $77.30  
  Purchase #2 $186.42   3.217%   $192.4171   $192.42   $192.40   $192.40  
  Purchase #3 $13.60   6.488%   $14.4824   $14.48   $14.50   $14.50  
  Purchase #4 $206.29   11.137%   $229.2645   $229.26   $229.25   $229.30  
  Purchase #5 $190.44   10.512%   $210.4591   $210.46   $210.45   $210.50  
  Purchase #6 $91.44   4.673%   $95.713   $95.71   $95.70   $95.70  
  Purchase #7 $186.59   8.629%   $202.6909   $202.69   $202.70   $202.70  
  7 purchase totals = $947.19       $1,022.3493   $1,022.34   $1,022.30   $1,022.40