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 $217.41   6.332%   $231.1764   $231.18   $231.20   $231.20  
  Purchase #2 $189.90   6.668%   $202.5625   $202.56   $202.55   $202.60  
  Purchase #3 $70.57   10.202%   $77.7696   $77.77   $77.75   $77.80  
  Purchase #4 $119.79   5.720%   $126.642   $126.64   $126.65   $126.60  
  Purchase #5 $140.31   13.188%   $158.8141   $158.81   $158.80   $158.80  
  Purchase #6 $68.37   13.132%   $77.3483   $77.35   $77.35   $77.30  
  Purchase #7 $130.40   13.385%   $147.854   $147.85   $147.85   $147.90  
  7 purchase totals = $936.75       $1,022.1669   $1,022.16   $1,022.15   $1,022.20