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 $125.29   4.345%   $130.7339   $130.73   $130.75   $130.70  
  Purchase #2 $67.48   5.493%   $71.1867   $71.19   $71.20   $71.20  
  Purchase #3 $47.95   8.645%   $52.0953   $52.10   $52.10   $52.10  
  Purchase #4 $250.37   4.516%   $261.6767   $261.68   $261.70   $261.70  
  Purchase #5 $165.53   9.865%   $181.8595   $181.86   $181.85   $181.90  
  Purchase #6 $168.56   9.277%   $184.1973   $184.20   $184.20   $184.20  
  Purchase #7 $173.46   8.128%   $187.5588   $187.56   $187.55   $187.60  
  7 purchase totals = $998.64       $1,069.3082   $1,069.32   $1,069.35   $1,069.40