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 $204.27   13.711%   $232.2775   $232.28   $232.30   $232.30  
  Purchase #2 $155.67   8.182%   $168.4069   $168.41   $168.40   $168.40  
  Purchase #3 $183.50   13.873%   $208.957   $208.96   $208.95   $209.00  
  Purchase #4 $229.54   6.811%   $245.174   $245.17   $245.15   $245.20  
  Purchase #5 $191.85   12.409%   $215.6567   $215.66   $215.65   $215.70  
  Purchase #6 $151.49   12.428%   $170.3172   $170.32   $170.30   $170.30  
  Purchase #7 $166.59   3.800%   $172.9204   $172.92   $172.90   $172.90  
  7 purchase totals = $1,282.91       $1,413.7097   $1,413.72   $1,413.65   $1,413.80