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 $162.64   3.442%   $168.2381   $168.24   $168.25   $168.20  
  Purchase #2 $60.66   11.856%   $67.8518   $67.85   $67.85   $67.90  
  Purchase #3 $32.34   4.683%   $33.8545   $33.85   $33.85   $33.90  
  Purchase #4 $217.62   12.267%   $244.3154   $244.32   $244.30   $244.30  
  Purchase #5 $26.55   11.196%   $29.5225   $29.52   $29.50   $29.50  
  Purchase #6 $68.65   12.217%   $77.037   $77.04   $77.05   $77.00  
  Purchase #7 $176.66   4.820%   $185.175   $185.18   $185.20   $185.20  
  7 purchase totals = $745.12       $805.9943   $806.00   $806.00   $806.00