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 $223.84   8.519%   $242.9089   $242.91   $242.90   $242.90  
  Purchase #2 $14.97   13.464%   $16.9856   $16.99   $17.00   $17.00  
  Purchase #3 $104.44   6.655%   $111.3905   $111.39   $111.40   $111.40  
  Purchase #4 $176.34   11.558%   $196.7214   $196.72   $196.70   $196.70  
  Purchase #5 $95.52   10.655%   $105.6977   $105.70   $105.70   $105.70  
  Purchase #6 $183.28   9.728%   $201.1095   $201.11   $201.10   $201.10  
  Purchase #7 $116.84   4.681%   $122.3093   $122.31   $122.30   $122.30  
  7 purchase totals = $915.23       $997.1229   $997.13   $997.10   $997.10