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 $215.61   9.785%   $236.7074   $236.71   $236.70   $236.70  
  Purchase #2 $106.72   11.448%   $118.9373   $118.94   $118.95   $118.90  
  Purchase #3 $84.68   4.635%   $88.6049   $88.60   $88.60   $88.60  
  Purchase #4 $210.62   9.463%   $230.551   $230.55   $230.55   $230.60  
  Purchase #5 $155.99   4.630%   $163.2123   $163.21   $163.20   $163.20  
  Purchase #6 $196.98   11.837%   $220.2965   $220.30   $220.30   $220.30  
  Purchase #7 $84.36   4.395%   $88.0676   $88.07   $88.05   $88.10  
  7 purchase totals = $1,054.96       $1,146.3770   $1,146.38   $1,146.35   $1,146.40