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 $205.84   9.819%   $226.0514   $226.05   $226.05   $226.10  
  Purchase #2 $179.82   12.181%   $201.7239   $201.72   $201.70   $201.70  
  Purchase #3 $87.88   5.652%   $92.847   $92.85   $92.85   $92.80  
  Purchase #4 $111.78   3.234%   $115.395   $115.40   $115.40   $115.40  
  Purchase #5 $62.86   13.316%   $71.2304   $71.23   $71.25   $71.20  
  Purchase #6 $170.44   3.790%   $176.8997   $176.90   $176.90   $176.90  
  Purchase #7 $39.84   5.128%   $41.883   $41.88   $41.90   $41.90  
  7 purchase totals = $858.46       $926.0304   $926.03   $926.05   $926.00