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 $95.82   8.235%   $103.7108   $103.71   $103.70   $103.70  
  Purchase #2 $250.92   13.803%   $285.5545   $285.55   $285.55   $285.60  
  Purchase #3 $84.50   8.452%   $91.6419   $91.64   $91.65   $91.60  
  Purchase #4 $234.33   5.506%   $247.2322   $247.23   $247.25   $247.20  
  Purchase #5 $106.33   8.356%   $115.2149   $115.21   $115.20   $115.20  
  Purchase #6 $71.69   8.675%   $77.9091   $77.91   $77.90   $77.90  
  Purchase #7 $31.50   6.341%   $33.4974   $33.50   $33.50   $33.50  
  7 purchase totals = $875.09       $954.7608   $954.75   $954.75   $954.70