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 $148.96   4.696%   $155.9552   $155.96   $155.95   $156.00  
  Purchase #2 $228.30   5.551%   $240.9729   $240.97   $240.95   $241.00  
  Purchase #3 $75.48   8.729%   $82.0686   $82.07   $82.05   $82.10  
  Purchase #4 $173.66   5.255%   $182.7858   $182.79   $182.80   $182.80  
  Purchase #5 $245.41   4.858%   $257.332   $257.33   $257.35   $257.30  
  Purchase #6 $162.68   11.653%   $181.6371   $181.64   $181.65   $181.60  
  Purchase #7 $245.89   3.492%   $254.4765   $254.48   $254.50   $254.50  
  7 purchase totals = $1,280.38       $1,355.2281   $1,355.24   $1,355.25   $1,355.30