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 $68.46   4.659%   $71.6496   $71.65   $71.65   $71.60  
  Purchase #2 $167.53   10.740%   $185.5227   $185.52   $185.50   $185.50  
  Purchase #3 $127.40   8.464%   $138.1831   $138.18   $138.20   $138.20  
  Purchase #4 $181.60   8.864%   $197.697   $197.70   $197.70   $197.70  
  Purchase #5 $164.77   3.491%   $170.5221   $170.52   $170.50   $170.50  
  Purchase #6 $45.67   13.565%   $51.8651   $51.87   $51.85   $51.90  
  Purchase #7 $46.93   12.561%   $52.8249   $52.82   $52.80   $52.80  
  7 purchase totals = $802.36       $868.2645   $868.26   $868.20   $868.20