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 $158.80   6.577%   $169.2443   $169.24   $169.25   $169.20  
  Purchase #2 $155.52   11.636%   $173.6163   $173.62   $173.60   $173.60  
  Purchase #3 $165.87   13.252%   $187.8511   $187.85   $187.85   $187.90  
  Purchase #4 $174.80   13.841%   $198.9941   $198.99   $199.00   $199.00  
  Purchase #5 $223.88   5.824%   $236.9188   $236.92   $236.90   $236.90  
  Purchase #6 $41.90   5.513%   $44.2099   $44.21   $44.20   $44.20  
  Purchase #7 $145.49   13.724%   $165.457   $165.46   $165.45   $165.50  
  7 purchase totals = $1,066.26       $1,176.2915   $1,176.29   $1,176.25   $1,176.30