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 $234.97   13.410%   $266.4795   $266.48   $266.50   $266.50  
  Purchase #2 $202.96   10.190%   $223.6416   $223.64   $223.65   $223.60  
  Purchase #3 $187.30   9.259%   $204.6421   $204.64   $204.65   $204.60  
  Purchase #4 $144.90   3.864%   $150.4989   $150.50   $150.50   $150.50  
  Purchase #5 $21.97   10.551%   $24.2881   $24.29   $24.30   $24.30  
  Purchase #6 $84.40   3.772%   $87.5836   $87.58   $87.60   $87.60  
  Purchase #7 $219.64   13.306%   $248.8653   $248.87   $248.85   $248.90  
  7 purchase totals = $1,096.14       $1,205.9991   $1,206.00   $1,206.05   $1,206.00