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 $71.31   3.255%   $73.6311   $73.63   $73.65   $73.60  
  Purchase #2 $34.61   8.775%   $37.647   $37.65   $37.65   $37.60  
  Purchase #3 $192.63   5.324%   $202.8856   $202.89   $202.90   $202.90  
  Purchase #4 $73.58   8.599%   $79.9071   $79.91   $79.90   $79.90  
  Purchase #5 $182.79   10.753%   $202.4454   $202.45   $202.45   $202.40  
  Purchase #6 $247.72   3.279%   $255.8427   $255.84   $255.85   $255.80  
  Purchase #7 $32.65   10.623%   $36.1184   $36.12   $36.10   $36.10  
  7 purchase totals = $835.29       $888.4773   $888.49   $888.50   $888.30