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 $8.32   7.819%   $8.9705   $8.97   $8.95   $9.00  
  Purchase #2 $12.74   3.825%   $13.2273   $13.23   $13.25   $13.20  
  Purchase #3 $50.73   5.106%   $53.3203   $53.32   $53.30   $53.30  
  Purchase #4 $80.86   6.129%   $85.8159   $85.82   $85.80   $85.80  
  Purchase #5 $163.52   3.482%   $169.2138   $169.21   $169.20   $169.20  
  Purchase #6 $62.49   6.246%   $66.3931   $66.39   $66.40   $66.40  
  Purchase #7 $83.27   11.598%   $92.9277   $92.93   $92.95   $92.90  
  7 purchase totals = $461.93       $489.8686   $489.87   $489.85   $489.80