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 $195.82   8.869%   $213.1873   $213.19   $213.20   $213.20  
  Purchase #2 $199.43   5.818%   $211.0328   $211.03   $211.05   $211.00  
  Purchase #3 $157.47   3.433%   $162.8759   $162.88   $162.90   $162.90  
  Purchase #4 $33.81   8.610%   $36.721   $36.72   $36.70   $36.70  
  Purchase #5 $217.32   3.225%   $224.3286   $224.33   $224.35   $224.30  
  Purchase #6 $137.85   5.287%   $145.1381   $145.14   $145.15   $145.10  
  Purchase #7 $36.78   3.213%   $37.9617   $37.96   $37.95   $38.00  
  7 purchase totals = $978.48       $1,031.2454   $1,031.25   $1,031.30   $1,031.20