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 $160.53   8.593%   $174.3243   $174.32   $174.30   $174.30  
  Purchase #2 $51.46   12.618%   $57.9532   $57.95   $57.95   $58.00  
  Purchase #3 $165.44   6.373%   $175.9835   $175.98   $176.00   $176.00  
  Purchase #4 $183.90   8.760%   $200.0096   $200.01   $200.00   $200.00  
  Purchase #5 $32.68   8.203%   $35.3607   $35.36   $35.35   $35.40  
  Purchase #6 $76.75   6.496%   $81.7357   $81.74   $81.75   $81.70  
  Purchase #7 $116.46   8.788%   $126.6945   $126.69   $126.70   $126.70  
  7 purchase totals = $787.22       $852.0615   $852.05   $852.05   $852.10