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 $40.62   6.723%   $43.3509   $43.35   $43.35   $43.40  
  Purchase #2 $168.50   7.544%   $181.2116   $181.21   $181.20   $181.20  
  Purchase #3 $250.90   13.465%   $284.6837   $284.68   $284.70   $284.70  
  Purchase #4 $59.41   11.286%   $66.115   $66.12   $66.10   $66.10  
  Purchase #5 $177.62   5.745%   $187.8243   $187.82   $187.80   $187.80  
  Purchase #6 $199.39   10.405%   $220.1365   $220.14   $220.15   $220.10  
  Purchase #7 $62.90   6.697%   $67.1124   $67.11   $67.10   $67.10  
  7 purchase totals = $959.34       $1,050.4344   $1,050.43   $1,050.40   $1,050.40