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 $168.68   13.592%   $191.607   $191.61   $191.60   $191.60  
  Purchase #2 $65.52   9.147%   $71.5131   $71.51   $71.50   $71.50  
  Purchase #3 $242.87   7.128%   $260.1818   $260.18   $260.20   $260.20  
  Purchase #4 $195.68   3.865%   $203.243   $203.24   $203.25   $203.20  
  Purchase #5 $49.41   8.590%   $53.6543   $53.65   $53.65   $53.70  
  Purchase #6 $189.73   6.743%   $202.5235   $202.52   $202.50   $202.50  
  Purchase #7 $216.63   4.380%   $226.1184   $226.12   $226.10   $226.10  
  7 purchase totals = $1,128.52       $1,208.8411   $1,208.83   $1,208.80   $1,208.80