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 $84.39   8.765%   $91.7868   $91.79   $91.80   $91.80  
  Purchase #2 $181.95   10.119%   $200.3615   $200.36   $200.35   $200.40  
  Purchase #3 $178.53   4.831%   $187.1548   $187.15   $187.15   $187.20  
  Purchase #4 $26.96   6.328%   $28.666   $28.67   $28.65   $28.70  
  Purchase #5 $200.47   13.430%   $227.3931   $227.39   $227.40   $227.40  
  Purchase #6 $107.65   10.469%   $118.9199   $118.92   $118.90   $118.90  
  Purchase #7 $237.91   9.785%   $261.1895   $261.19   $261.20   $261.20  
  7 purchase totals = $1,017.86       $1,115.4716   $1,115.47   $1,115.45   $1,115.60