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 $174.57   12.196%   $195.8606   $195.86   $195.85   $195.90  
  Purchase #2 $85.42   7.469%   $91.8   $91.80   $91.80   $91.80  
  Purchase #3 $87.77   11.563%   $97.9188   $97.92   $97.90   $97.90  
  Purchase #4 $187.26   10.802%   $207.4878   $207.49   $207.50   $207.50  
  Purchase #5 $57.76   6.644%   $61.5976   $61.60   $61.60   $61.60  
  Purchase #6 $123.76   3.739%   $128.3874   $128.39   $128.40   $128.40  
  Purchase #7 $73.52   13.222%   $83.2408   $83.24   $83.25   $83.20  
  7 purchase totals = $790.06       $866.2930   $866.30   $866.30   $866.30