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 $244.67   13.129%   $276.7927   $276.79   $276.80   $276.80  
  Purchase #2 $12.33   8.220%   $13.3435   $13.34   $13.35   $13.30  
  Purchase #3 $19.55   12.457%   $21.9853   $21.99   $22.00   $22.00  
  Purchase #4 $112.63   3.579%   $116.661   $116.66   $116.65   $116.70  
  Purchase #5 $189.36   13.283%   $214.5127   $214.51   $214.50   $214.50  
  Purchase #6 $163.84   6.255%   $174.0882   $174.09   $174.10   $174.10  
  Purchase #7 $247.93   12.278%   $278.3708   $278.37   $278.35   $278.40  
  7 purchase totals = $990.31       $1,095.7542   $1,095.75   $1,095.75   $1,095.80