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 $234.87   13.341%   $266.204   $266.20   $266.20   $266.20  
  Purchase #2 $83.44   4.339%   $87.0605   $87.06   $87.05   $87.10  
  Purchase #3 $85.37   5.284%   $89.881   $89.88   $89.90   $89.90  
  Purchase #4 $54.36   5.486%   $57.3422   $57.34   $57.35   $57.30  
  Purchase #5 $213.96   4.647%   $223.9027   $223.90   $223.90   $223.90  
  Purchase #6 $185.89   10.826%   $206.0145   $206.01   $206.00   $206.00  
  Purchase #7 $160.74   6.272%   $170.8216   $170.82   $170.80   $170.80  
  7 purchase totals = $1,018.63       $1,101.2265   $1,101.21   $1,101.20   $1,101.20