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 $249.98   5.754%   $264.3638   $264.36   $264.35   $264.40  
  Purchase #2 $83.27   12.636%   $93.792   $93.79   $93.80   $93.80  
  Purchase #3 $219.41   9.442%   $240.1267   $240.13   $240.15   $240.10  
  Purchase #4 $233.42   8.844%   $254.0637   $254.06   $254.05   $254.10  
  Purchase #5 $159.52   10.106%   $175.6411   $175.64   $175.65   $175.60  
  Purchase #6 $183.87   7.862%   $198.3259   $198.33   $198.35   $198.30  
  Purchase #7 $56.92   5.831%   $60.239   $60.24   $60.25   $60.20  
  7 purchase totals = $1,186.39       $1,286.5522   $1,286.55   $1,286.60   $1,286.50