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 $67.93   8.641%   $73.7998   $73.80   $73.80   $73.80  
  Purchase #2 $210.63   5.167%   $221.5133   $221.51   $221.50   $221.50  
  Purchase #3 $98.56   3.363%   $101.8746   $101.87   $101.85   $101.90  
  Purchase #4 $184.81   7.422%   $198.5266   $198.53   $198.55   $198.50  
  Purchase #5 $89.99   10.387%   $99.3373   $99.34   $99.35   $99.30  
  Purchase #6 $167.53   6.845%   $178.9974   $179.00   $179.00   $179.00  
  Purchase #7 $131.37   6.849%   $140.3675   $140.37   $140.35   $140.40  
  7 purchase totals = $950.82       $1,014.4165   $1,014.42   $1,014.40   $1,014.40