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 $118.61   7.617%   $127.6445   $127.64   $127.65   $127.60  
  Purchase #2 $177.28   13.542%   $201.2873   $201.29   $201.30   $201.30  
  Purchase #3 $96.33   6.283%   $102.3824   $102.38   $102.40   $102.40  
  Purchase #4 $50.42   8.201%   $54.5549   $54.55   $54.55   $54.60  
  Purchase #5 $123.62   9.491%   $135.3528   $135.35   $135.35   $135.40  
  Purchase #6 $92.45   8.499%   $100.3073   $100.31   $100.30   $100.30  
  Purchase #7 $17.32   8.789%   $18.8423   $18.84   $18.85   $18.80  
  7 purchase totals = $676.03       $740.3715   $740.36   $740.40   $740.40