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 $169.81   4.124%   $176.813   $176.81   $176.80   $176.80  
  Purchase #2 $165.62   6.582%   $176.5211   $176.52   $176.50   $176.50  
  Purchase #3 $62.84   13.858%   $71.5484   $71.55   $71.55   $71.50  
  Purchase #4 $56.44   12.684%   $63.5988   $63.60   $63.60   $63.60  
  Purchase #5 $89.89   3.393%   $92.94   $92.94   $92.95   $92.90  
  Purchase #6 $107.30   11.856%   $120.0215   $120.02   $120.00   $120.00  
  Purchase #7 $175.72   3.361%   $181.6259   $181.63   $181.65   $181.60  
  7 purchase totals = $827.62       $883.0687   $883.07   $883.05   $882.90