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 $175.98   6.791%   $187.9308   $187.93   $187.95   $187.90  
  Purchase #2 $95.90   11.197%   $106.6379   $106.64   $106.65   $106.60  
  Purchase #3 $206.35   8.683%   $224.2674   $224.27   $224.25   $224.30  
  Purchase #4 $75.58   9.198%   $82.5318   $82.53   $82.55   $82.50  
  Purchase #5 $135.38   5.517%   $142.8489   $142.85   $142.85   $142.80  
  Purchase #6 $197.75   3.691%   $205.049   $205.05   $205.05   $205.00  
  Purchase #7 $90.28   6.526%   $96.1717   $96.17   $96.15   $96.20  
  7 purchase totals = $977.22       $1,045.4375   $1,045.44   $1,045.45   $1,045.30