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 $197.53   4.478%   $206.3754   $206.38   $206.40   $206.40  
  Purchase #2 $75.87   13.726%   $86.2839   $86.28   $86.30   $86.30  
  Purchase #3 $107.49   13.490%   $121.9904   $121.99   $122.00   $122.00  
  Purchase #4 $186.92   13.297%   $211.7748   $211.77   $211.75   $211.80  
  Purchase #5 $214.52   13.345%   $243.1477   $243.15   $243.15   $243.10  
  Purchase #6 $167.32   9.423%   $183.0866   $183.09   $183.10   $183.10  
  Purchase #7 $22.37   11.135%   $24.8609   $24.86   $24.85   $24.90  
  7 purchase totals = $972.02       $1,077.5197   $1,077.52   $1,077.55   $1,077.60