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 $89.39   6.505%   $95.2048   $95.20   $95.20   $95.20  
  Purchase #2 $44.64   10.423%   $49.2928   $49.29   $49.30   $49.30  
  Purchase #3 $43.44   4.671%   $45.4691   $45.47   $45.45   $45.50  
  Purchase #4 $23.60   6.759%   $25.1951   $25.20   $25.20   $25.20  
  Purchase #5 $98.51   6.818%   $105.2264   $105.23   $105.25   $105.20  
  Purchase #6 $239.34   9.478%   $262.0246   $262.02   $262.00   $262.00  
  Purchase #7 $223.40   10.841%   $247.6188   $247.62   $247.60   $247.60  
  7 purchase totals = $762.32       $830.0316   $830.03   $830.00   $830.00