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 $58.30   5.706%   $61.6266   $61.63   $61.65   $61.60  
  Purchase #2 $182.27   11.194%   $202.6733   $202.67   $202.65   $202.70  
  Purchase #3 $245.96   11.592%   $274.4717   $274.47   $274.45   $274.50  
  Purchase #4 $88.51   5.547%   $93.4196   $93.42   $93.40   $93.40  
  Purchase #5 $116.63   4.609%   $122.0055   $122.01   $122.00   $122.00  
  Purchase #6 $34.36   4.216%   $35.8086   $35.81   $35.80   $35.80  
  Purchase #7 $247.38   4.179%   $257.718   $257.72   $257.70   $257.70  
  7 purchase totals = $973.41       $1,047.7233   $1,047.73   $1,047.65   $1,047.70