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 $113.50   4.433%   $118.5315   $118.53   $118.55   $118.50  
  Purchase #2 $190.83   11.348%   $212.4854   $212.49   $212.50   $212.50  
  Purchase #3 $62.66   9.775%   $68.785   $68.79   $68.80   $68.80  
  Purchase #4 $245.62   8.338%   $266.0998   $266.10   $266.10   $266.10  
  Purchase #5 $147.80   12.670%   $166.5263   $166.53   $166.55   $166.50  
  Purchase #6 $30.98   10.665%   $34.284   $34.28   $34.30   $34.30  
  Purchase #7 $204.81   5.498%   $216.0705   $216.07   $216.05   $216.10  
  7 purchase totals = $996.20       $1,082.7825   $1,082.79   $1,082.85   $1,082.80