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 $93.73   10.642%   $103.7047   $103.70   $103.70   $103.70  
  Purchase #2 $79.59   9.581%   $87.2155   $87.22   $87.20   $87.20  
  Purchase #3 $41.58   6.519%   $44.2906   $44.29   $44.30   $44.30  
  Purchase #4 $154.81   4.664%   $162.0303   $162.03   $162.05   $162.00  
  Purchase #5 $48.61   4.229%   $50.6657   $50.67   $50.65   $50.70  
  Purchase #6 $221.59   11.653%   $247.4119   $247.41   $247.40   $247.40  
  Purchase #7 $43.26   8.405%   $46.896   $46.90   $46.90   $46.90  
  7 purchase totals = $683.17       $742.2147   $742.22   $742.20   $742.20