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 $49.41   13.837%   $56.2469   $56.25   $56.25   $56.20  
  Purchase #2 $250.91   3.132%   $258.7685   $258.77   $258.75   $258.80  
  Purchase #3 $69.91   4.727%   $73.2146   $73.21   $73.20   $73.20  
  Purchase #4 $167.71   3.614%   $173.771   $173.77   $173.75   $173.80  
  Purchase #5 $143.97   8.249%   $155.8461   $155.85   $155.85   $155.80  
  Purchase #6 $145.81   8.641%   $158.4094   $158.41   $158.40   $158.40  
  Purchase #7 $173.59   12.159%   $194.6968   $194.70   $194.70   $194.70  
  7 purchase totals = $1,001.31       $1,070.9533   $1,070.96   $1,070.90   $1,070.90