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 $164.82   8.792%   $179.311   $179.31   $179.30   $179.30  
  Purchase #2 $116.42   8.222%   $125.9921   $125.99   $126.00   $126.00  
  Purchase #3 $70.65   4.567%   $73.8766   $73.88   $73.90   $73.90  
  Purchase #4 $106.34   4.732%   $111.372   $111.37   $111.35   $111.40  
  Purchase #5 $73.98   6.825%   $79.0291   $79.03   $79.05   $79.00  
  Purchase #6 $205.87   8.392%   $223.1466   $223.15   $223.15   $223.10  
  Purchase #7 $65.41   3.409%   $67.6398   $67.64   $67.65   $67.60  
  7 purchase totals = $803.49       $860.3672   $860.37   $860.40   $860.30