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 $60.34   13.795%   $68.6639   $68.66   $68.65   $68.70  
  Purchase #2 $159.89   4.468%   $167.0339   $167.03   $167.05   $167.00  
  Purchase #3 $114.46   3.367%   $118.3139   $118.31   $118.30   $118.30  
  Purchase #4 $26.26   6.565%   $27.984   $27.98   $28.00   $28.00  
  Purchase #5 $247.49   13.256%   $280.2973   $280.30   $280.30   $280.30  
  Purchase #6 $80.85   7.549%   $86.9534   $86.95   $86.95   $87.00  
  Purchase #7 $94.59   8.714%   $102.8326   $102.83   $102.85   $102.80  
  7 purchase totals = $783.88       $852.0790   $852.06   $852.10   $852.10