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 $246.78   8.366%   $267.4256   $267.43   $267.45   $267.40  
  Purchase #2 $105.35   10.267%   $116.1663   $116.17   $116.15   $116.20  
  Purchase #3 $82.27   8.773%   $89.4875   $89.49   $89.50   $89.50  
  Purchase #4 $72.52   4.541%   $75.8131   $75.81   $75.80   $75.80  
  Purchase #5 $178.85   8.591%   $194.215   $194.22   $194.20   $194.20  
  Purchase #6 $74.31   11.157%   $82.6008   $82.60   $82.60   $82.60  
  Purchase #7 $188.40   8.345%   $204.122   $204.12   $204.10   $204.10  
  7 purchase totals = $948.48       $1,029.8303   $1,029.84   $1,029.80   $1,029.80