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 $167.94   10.476%   $185.5334   $185.53   $185.55   $185.50  
  Purchase #2 $143.44   13.872%   $163.338   $163.34   $163.35   $163.30  
  Purchase #3 $97.75   4.355%   $102.007   $102.01   $102.00   $102.00  
  Purchase #4 $151.98   11.248%   $169.0747   $169.07   $169.05   $169.10  
  Purchase #5 $219.25   7.736%   $236.2112   $236.21   $236.20   $236.20  
  Purchase #6 $227.75   5.488%   $240.2489   $240.25   $240.25   $240.20  
  Purchase #7 $160.70   5.555%   $169.6269   $169.63   $169.65   $169.60  
  7 purchase totals = $1,168.81       $1,266.0401   $1,266.04   $1,266.05   $1,265.90