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 $29.34   5.416%   $30.9291   $30.93   $30.95   $30.90  
  Purchase #2 $18.26   10.164%   $20.1159   $20.12   $20.10   $20.10  
  Purchase #3 $9.83   3.715%   $10.1952   $10.20   $10.20   $10.20  
  Purchase #4 $98.70   13.873%   $112.3927   $112.39   $112.40   $112.40  
  Purchase #5 $36.62   8.740%   $39.8206   $39.82   $39.80   $39.80  
  Purchase #6 $15.66   3.205%   $16.1619   $16.16   $16.15   $16.20  
  Purchase #7 $212.32   7.716%   $228.7026   $228.70   $228.70   $228.70  
  7 purchase totals = $420.73       $458.3180   $458.32   $458.30   $458.30