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 $58.97   13.185%   $66.7452   $66.75   $66.75   $66.70  
  Purchase #2 $210.28   8.499%   $228.1517   $228.15   $228.15   $228.20  
  Purchase #3 $230.52   5.443%   $243.0672   $243.07   $243.05   $243.10  
  Purchase #4 $205.37   7.826%   $221.4423   $221.44   $221.45   $221.40  
  Purchase #5 $116.42   5.659%   $123.0082   $123.01   $123.00   $123.00  
  Purchase #6 $108.52   5.711%   $114.7176   $114.72   $114.70   $114.70  
  Purchase #7 $147.75   6.373%   $157.1661   $157.17   $157.15   $157.20  
  7 purchase totals = $1,077.83       $1,154.2983   $1,154.31   $1,154.25   $1,154.30