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 $113.41   7.554%   $121.977   $121.98   $122.00   $122.00  
  Purchase #2 $234.82   8.680%   $255.2024   $255.20   $255.20   $255.20  
  Purchase #3 $81.54   7.195%   $87.4068   $87.41   $87.40   $87.40  
  Purchase #4 $185.41   9.551%   $203.1185   $203.12   $203.10   $203.10  
  Purchase #5 $57.48   3.258%   $59.3527   $59.35   $59.35   $59.40  
  Purchase #6 $147.42   9.255%   $161.0637   $161.06   $161.05   $161.10  
  Purchase #7 $119.82   12.601%   $134.9185   $134.92   $134.90   $134.90  
  7 purchase totals = $939.90       $1,023.0396   $1,023.04   $1,023.00   $1,023.10