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 $121.87   3.421%   $126.0392   $126.04   $126.05   $126.00  
  Purchase #2 $23.55   10.162%   $25.9432   $25.94   $25.95   $25.90  
  Purchase #3 $50.29   5.307%   $52.9589   $52.96   $52.95   $53.00  
  Purchase #4 $140.41   11.162%   $156.0826   $156.08   $156.10   $156.10  
  Purchase #5 $204.73   8.785%   $222.7155   $222.72   $222.70   $222.70  
  Purchase #6 $165.26   7.325%   $177.3653   $177.37   $177.35   $177.40  
  Purchase #7 $13.37   9.520%   $14.6428   $14.64   $14.65   $14.60  
  7 purchase totals = $719.48       $775.7475   $775.75   $775.75   $775.70