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 $157.81   10.283%   $174.0376   $174.04   $174.05   $174.00  
  Purchase #2 $158.53   7.752%   $170.8192   $170.82   $170.80   $170.80  
  Purchase #3 $37.63   11.407%   $41.9225   $41.92   $41.90   $41.90  
  Purchase #4 $49.52   7.617%   $53.2919   $53.29   $53.30   $53.30  
  Purchase #5 $65.29   3.691%   $67.6999   $67.70   $67.70   $67.70  
  Purchase #6 $190.67   5.525%   $201.2045   $201.20   $201.20   $201.20  
  Purchase #7 $107.94   9.167%   $117.8349   $117.83   $117.85   $117.80  
  7 purchase totals = $767.39       $826.8105   $826.80   $826.80   $826.70