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 $61.54   13.791%   $70.027   $70.03   $70.05   $70.00  
  Purchase #2 $103.53   7.262%   $111.0483   $111.05   $111.05   $111.00  
  Purchase #3 $133.68   10.626%   $147.8848   $147.88   $147.90   $147.90  
  Purchase #4 $156.70   3.416%   $162.0529   $162.05   $162.05   $162.10  
  Purchase #5 $223.39   9.433%   $244.4624   $244.46   $244.45   $244.50  
  Purchase #6 $33.85   7.231%   $36.2977   $36.30   $36.30   $36.30  
  Purchase #7 $66.96   10.486%   $73.9814   $73.98   $74.00   $74.00  
  7 purchase totals = $779.65       $845.7545   $845.75   $845.80   $845.80