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 $248.35   13.758%   $282.518   $282.52   $282.50   $282.50  
  Purchase #2 $34.34   8.694%   $37.3255   $37.33   $37.35   $37.30  
  Purchase #3 $51.77   5.644%   $54.6919   $54.69   $54.70   $54.70  
  Purchase #4 $143.85   4.774%   $150.7174   $150.72   $150.70   $150.70  
  Purchase #5 $110.52   10.212%   $121.8063   $121.81   $121.80   $121.80  
  Purchase #6 $28.98   3.708%   $30.0546   $30.05   $30.05   $30.10  
  Purchase #7 $45.25   7.340%   $48.5714   $48.57   $48.55   $48.60  
  7 purchase totals = $663.06       $725.6851   $725.69   $725.65   $725.70