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 $51.39   8.639%   $55.8296   $55.83   $55.85   $55.80  
  Purchase #2 $239.82   6.830%   $256.1997   $256.20   $256.20   $256.20  
  Purchase #3 $228.37   7.356%   $245.1689   $245.17   $245.15   $245.20  
  Purchase #4 $226.70   11.686%   $253.1922   $253.19   $253.20   $253.20  
  Purchase #5 $58.76   8.410%   $63.7017   $63.70   $63.70   $63.70  
  Purchase #6 $233.80   4.796%   $245.013   $245.01   $245.00   $245.00  
  Purchase #7 $244.35   13.812%   $278.0996   $278.10   $278.10   $278.10  
  7 purchase totals = $1,283.19       $1,397.2047   $1,397.20   $1,397.20   $1,397.20