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 $156.28   13.797%   $177.842   $177.84   $177.85   $177.80  
  Purchase #2 $181.29   10.622%   $200.5466   $200.55   $200.55   $200.50  
  Purchase #3 $12.27   10.328%   $13.5372   $13.54   $13.55   $13.50  
  Purchase #4 $162.73   10.593%   $179.968   $179.97   $179.95   $180.00  
  Purchase #5 $178.69   8.695%   $194.2271   $194.23   $194.25   $194.20  
  Purchase #6 $111.33   5.308%   $117.2394   $117.24   $117.25   $117.20  
  Purchase #7 $57.70   6.274%   $61.3201   $61.32   $61.30   $61.30  
  7 purchase totals = $860.29       $944.6804   $944.69   $944.70   $944.50