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 $54.68   7.221%   $58.6284   $58.63   $58.65   $58.60  
  Purchase #2 $159.37   9.402%   $174.354   $174.35   $174.35   $174.40  
  Purchase #3 $226.33   11.802%   $253.0415   $253.04   $253.05   $253.00  
  Purchase #4 $96.26   7.706%   $103.6778   $103.68   $103.70   $103.70  
  Purchase #5 $98.58   8.176%   $106.6399   $106.64   $106.65   $106.60  
  Purchase #6 $147.63   12.199%   $165.6394   $165.64   $165.65   $165.60  
  Purchase #7 $82.58   12.177%   $92.6358   $92.64   $92.65   $92.60  
  7 purchase totals = $865.43       $954.6168   $954.62   $954.70   $954.50