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 $125.61   7.481%   $135.0069   $135.01   $135.00   $135.00  
  Purchase #2 $29.78   7.495%   $32.012   $32.01   $32.00   $32.00  
  Purchase #3 $145.91   6.194%   $154.9477   $154.95   $154.95   $154.90  
  Purchase #4 $86.59   12.262%   $97.2077   $97.21   $97.20   $97.20  
  Purchase #5 $73.49   6.873%   $78.541   $78.54   $78.55   $78.50  
  Purchase #6 $142.51   6.159%   $151.2872   $151.29   $151.30   $151.30  
  Purchase #7 $141.44   4.170%   $147.338   $147.34   $147.35   $147.30  
  7 purchase totals = $745.33       $796.3405   $796.35   $796.35   $796.20