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 $167.96   5.274%   $176.8182   $176.82   $176.80   $176.80  
  Purchase #2 $163.85   9.414%   $179.2748   $179.27   $179.25   $179.30  
  Purchase #3 $145.46   3.727%   $150.8813   $150.88   $150.90   $150.90  
  Purchase #4 $188.76   11.780%   $210.9959   $211.00   $211.00   $211.00  
  Purchase #5 $51.86   10.604%   $57.3592   $57.36   $57.35   $57.40  
  Purchase #6 $62.66   11.776%   $70.0388   $70.04   $70.05   $70.00  
  Purchase #7 $169.41   4.459%   $176.964   $176.96   $176.95   $177.00  
  7 purchase totals = $949.96       $1,022.3322   $1,022.33   $1,022.30   $1,022.40