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 $68.63   8.198%   $74.2563   $74.26   $74.25   $74.30  
  Purchase #2 $58.82   5.127%   $61.8357   $61.84   $61.85   $61.80  
  Purchase #3 $181.39   11.175%   $201.6603   $201.66   $201.65   $201.70  
  Purchase #4 $47.40   6.737%   $50.5933   $50.59   $50.60   $50.60  
  Purchase #5 $85.37   10.847%   $94.6301   $94.63   $94.65   $94.60  
  Purchase #6 $34.76   6.866%   $37.1466   $37.15   $37.15   $37.10  
  Purchase #7 $92.60   7.478%   $99.5246   $99.52   $99.50   $99.50  
  7 purchase totals = $568.97       $619.6469   $619.65   $619.65   $619.60