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 $237.64   12.644%   $267.6872   $267.69   $267.70   $267.70  
  Purchase #2 $15.47   6.558%   $16.4845   $16.48   $16.50   $16.50  
  Purchase #3 $61.62   9.310%   $67.3568   $67.36   $67.35   $67.40  
  Purchase #4 $178.35   4.702%   $186.736   $186.74   $186.75   $186.70  
  Purchase #5 $82.30   13.198%   $93.162   $93.16   $93.15   $93.20  
  Purchase #6 $133.91   5.288%   $140.9912   $140.99   $141.00   $141.00  
  Purchase #7 $235.84   6.405%   $250.9456   $250.95   $250.95   $250.90  
  7 purchase totals = $945.13       $1,023.3633   $1,023.37   $1,023.40   $1,023.40