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 $47.65   5.332%   $50.1907   $50.19   $50.20   $50.20  
  Purchase #2 $219.77   10.276%   $242.3536   $242.35   $242.35   $242.40  
  Purchase #3 $104.57   13.416%   $118.5991   $118.60   $118.60   $118.60  
  Purchase #4 $97.41   11.389%   $108.504   $108.50   $108.50   $108.50  
  Purchase #5 $124.25   6.207%   $131.9622   $131.96   $131.95   $132.00  
  Purchase #6 $235.42   11.142%   $261.6505   $261.65   $261.65   $261.70  
  Purchase #7 $197.68   13.188%   $223.75   $223.75   $223.75   $223.80  
  7 purchase totals = $1,026.75       $1,137.0101   $1,137.00   $1,137.00   $1,137.20