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 $227.91   8.842%   $248.0618   $248.06   $248.05   $248.10  
  Purchase #2 $32.37   13.491%   $36.737   $36.74   $36.75   $36.70  
  Purchase #3 $43.45   5.348%   $45.7737   $45.77   $45.75   $45.80  
  Purchase #4 $80.73   13.640%   $91.7416   $91.74   $91.75   $91.70  
  Purchase #5 $5.80   4.131%   $6.0396   $6.04   $6.05   $6.00  
  Purchase #6 $244.84   9.424%   $267.9137   $267.91   $267.90   $267.90  
  Purchase #7 $226.96   12.331%   $254.9464   $254.95   $254.95   $254.90  
  7 purchase totals = $862.06       $951.2138   $951.21   $951.20   $951.10