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 $151.61   11.483%   $169.0194   $169.02   $169.00   $169.00  
  Purchase #2 $160.59   6.802%   $171.5133   $171.51   $171.50   $171.50  
  Purchase #3 $236.86   3.608%   $245.4059   $245.41   $245.40   $245.40  
  Purchase #4 $24.27   8.315%   $26.2881   $26.29   $26.30   $26.30  
  Purchase #5 $81.49   3.473%   $84.3201   $84.32   $84.30   $84.30  
  Purchase #6 $132.92   4.205%   $138.5093   $138.51   $138.50   $138.50  
  Purchase #7 $171.73   7.813%   $185.1473   $185.15   $185.15   $185.10  
  7 purchase totals = $959.47       $1,020.2034   $1,020.21   $1,020.15   $1,020.10