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 $12.54   13.695%   $14.2574   $14.26   $14.25   $14.30  
  Purchase #2 $85.80   9.337%   $93.8111   $93.81   $93.80   $93.80  
  Purchase #3 $104.34   11.559%   $116.4007   $116.40   $116.40   $116.40  
  Purchase #4 $45.60   8.242%   $49.3584   $49.36   $49.35   $49.40  
  Purchase #5 $245.51   9.371%   $268.5167   $268.52   $268.50   $268.50  
  Purchase #6 $157.62   13.212%   $178.4448   $178.44   $178.45   $178.40  
  Purchase #7 $80.56   6.353%   $85.678   $85.68   $85.70   $85.70  
  7 purchase totals = $731.97       $806.4671   $806.47   $806.45   $806.50