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 $106.38   9.769%   $116.7723   $116.77   $116.75   $116.80  
  Purchase #2 $19.48   6.839%   $20.8122   $20.81   $20.80   $20.80  
  Purchase #3 $194.31   7.250%   $208.3975   $208.40   $208.40   $208.40  
  Purchase #4 $158.48   7.257%   $169.9809   $169.98   $170.00   $170.00  
  Purchase #5 $176.81   7.147%   $189.4466   $189.45   $189.45   $189.40  
  Purchase #6 $158.80   4.314%   $165.6506   $165.65   $165.65   $165.70  
  Purchase #7 $179.85   5.206%   $189.213   $189.21   $189.20   $189.20  
  7 purchase totals = $994.11       $1,060.2731   $1,060.27   $1,060.25   $1,060.30