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 $156.81   12.616%   $176.5931   $176.59   $176.60   $176.60  
  Purchase #2 $103.40   12.234%   $116.05   $116.05   $116.05   $116.10  
  Purchase #3 $54.61   7.842%   $58.8925   $58.89   $58.90   $58.90  
  Purchase #4 $152.65   3.215%   $157.5577   $157.56   $157.55   $157.60  
  Purchase #5 $119.37   4.146%   $124.3191   $124.32   $124.30   $124.30  
  Purchase #6 $182.57   9.505%   $199.9233   $199.92   $199.90   $199.90  
  Purchase #7 $180.29   11.458%   $200.9476   $200.95   $200.95   $200.90  
  7 purchase totals = $949.70       $1,034.2833   $1,034.28   $1,034.25   $1,034.30