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 $48.61   12.453%   $54.6634   $54.66   $54.65   $54.70  
  Purchase #2 $183.27   9.711%   $201.0673   $201.07   $201.05   $201.10  
  Purchase #3 $237.66   9.743%   $260.8152   $260.82   $260.80   $260.80  
  Purchase #4 $85.66   13.349%   $97.0948   $97.09   $97.10   $97.10  
  Purchase #5 $12.91   3.860%   $13.4083   $13.41   $13.40   $13.40  
  Purchase #6 $65.28   12.660%   $73.5444   $73.54   $73.55   $73.50  
  Purchase #7 $220.42   9.791%   $242.0013   $242.00   $242.00   $242.00  
  7 purchase totals = $853.81       $942.5947   $942.59   $942.55   $942.60