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 $228.72   13.791%   $260.2628   $260.26   $260.25   $260.30  
  Purchase #2 $170.54   9.847%   $187.3331   $187.33   $187.35   $187.30  
  Purchase #3 $203.72   10.310%   $224.7235   $224.72   $224.70   $224.70  
  Purchase #4 $92.30   3.666%   $95.6837   $95.68   $95.70   $95.70  
  Purchase #5 $25.42   3.246%   $26.2451   $26.25   $26.25   $26.20  
  Purchase #6 $211.93   5.828%   $224.2813   $224.28   $224.30   $224.30  
  Purchase #7 $8.58   5.266%   $9.0318   $9.03   $9.05   $9.00  
  7 purchase totals = $941.21       $1,027.5613   $1,027.55   $1,027.60   $1,027.50