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 $241.41   4.688%   $252.7273   $252.73   $252.75   $252.70  
  Purchase #2 $164.37   6.674%   $175.3401   $175.34   $175.35   $175.30  
  Purchase #3 $111.27   5.612%   $117.5145   $117.51   $117.50   $117.50  
  Purchase #4 $137.72   13.539%   $156.3659   $156.37   $156.35   $156.40  
  Purchase #5 $246.87   6.579%   $263.1116   $263.11   $263.10   $263.10  
  Purchase #6 $33.89   6.243%   $36.0058   $36.01   $36.00   $36.00  
  Purchase #7 $24.56   3.342%   $25.3808   $25.38   $25.40   $25.40  
  7 purchase totals = $960.09       $1,026.4460   $1,026.45   $1,026.45   $1,026.40