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 $233.96   13.550%   $265.6616   $265.66   $265.65   $265.70  
  Purchase #2 $56.31   3.548%   $58.3079   $58.31   $58.30   $58.30  
  Purchase #3 $163.74   12.278%   $183.844   $183.84   $183.85   $183.80  
  Purchase #4 $36.28   6.494%   $38.636   $38.64   $38.65   $38.60  
  Purchase #5 $158.41   8.373%   $171.6737   $171.67   $171.65   $171.70  
  Purchase #6 $171.47   4.355%   $178.9375   $178.94   $178.95   $178.90  
  Purchase #7 $52.68   9.385%   $57.624   $57.62   $57.60   $57.60  
  7 purchase totals = $872.85       $954.6847   $954.68   $954.65   $954.60