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 $23.34   8.229%   $25.2606   $25.26   $25.25   $25.30  
  Purchase #2 $69.29   8.243%   $75.0016   $75.00   $75.00   $75.00  
  Purchase #3 $99.84   9.802%   $109.6263   $109.63   $109.65   $109.60  
  Purchase #4 $181.53   9.115%   $198.0765   $198.08   $198.10   $198.10  
  Purchase #5 $12.46   12.321%   $13.9952   $14.00   $14.00   $14.00  
  Purchase #6 $7.48   7.317%   $8.0273   $8.03   $8.05   $8.00  
  Purchase #7 $172.41   6.785%   $184.108   $184.11   $184.10   $184.10  
  7 purchase totals = $566.35       $614.0955   $614.11   $614.15   $614.10