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 $211.59   10.695%   $234.2196   $234.22   $234.20   $234.20  
  Purchase #2 $117.83   5.687%   $124.531   $124.53   $124.55   $124.50  
  Purchase #3 $70.90   4.517%   $74.1026   $74.10   $74.10   $74.10  
  Purchase #4 $198.60   5.820%   $210.1585   $210.16   $210.15   $210.20  
  Purchase #5 $160.26   5.460%   $169.0102   $169.01   $169.00   $169.00  
  Purchase #6 $24.75   11.159%   $27.5119   $27.51   $27.50   $27.50  
  Purchase #7 $178.67   3.167%   $184.3285   $184.33   $184.35   $184.30  
  7 purchase totals = $962.60       $1,023.8623   $1,023.86   $1,023.85   $1,023.80