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 $77.96   13.528%   $88.5064   $88.51   $88.50   $88.50  
  Purchase #2 $235.62   11.862%   $263.5692   $263.57   $263.55   $263.60  
  Purchase #3 $29.38   5.862%   $31.1023   $31.10   $31.10   $31.10  
  Purchase #4 $224.87   8.328%   $243.5972   $243.60   $243.60   $243.60  
  Purchase #5 $183.98   5.559%   $194.2074   $194.21   $194.20   $194.20  
  Purchase #6 $166.45   6.115%   $176.6284   $176.63   $176.65   $176.60  
  Purchase #7 $177.35   4.435%   $185.2155   $185.22   $185.20   $185.20  
  7 purchase totals = $1,095.61       $1,182.8264   $1,182.84   $1,182.80   $1,182.80