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 $45.53   4.823%   $47.7259   $47.73   $47.75   $47.70  
  Purchase #2 $95.57   13.236%   $108.2196   $108.22   $108.20   $108.20  
  Purchase #3 $63.91   12.866%   $72.1327   $72.13   $72.15   $72.10  
  Purchase #4 $179.90   5.704%   $190.1615   $190.16   $190.15   $190.20  
  Purchase #5 $22.86   4.793%   $23.9557   $23.96   $23.95   $24.00  
  Purchase #6 $106.44   5.525%   $112.3208   $112.32   $112.30   $112.30  
  Purchase #7 $221.54   10.150%   $244.0263   $244.03   $244.05   $244.00  
  7 purchase totals = $735.75       $798.5425   $798.55   $798.55   $798.50