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 $95.63   10.150%   $105.3364   $105.34   $105.35   $105.30  
  Purchase #2 $6.33   11.292%   $7.0448   $7.04   $7.05   $7.00  
  Purchase #3 $17.26   4.870%   $18.1006   $18.10   $18.10   $18.10  
  Purchase #4 $203.54   8.252%   $220.3361   $220.34   $220.35   $220.30  
  Purchase #5 $127.83   12.465%   $143.764   $143.76   $143.75   $143.80  
  Purchase #6 $68.32   7.501%   $73.4447   $73.44   $73.45   $73.40  
  Purchase #7 $202.86   11.115%   $225.4079   $225.41   $225.40   $225.40  
  7 purchase totals = $721.77       $793.4345   $793.43   $793.45   $793.30