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 $61.76   13.132%   $69.8703   $69.87   $69.85   $69.90  
  Purchase #2 $152.26   6.816%   $162.638   $162.64   $162.65   $162.60  
  Purchase #3 $20.82   4.388%   $21.7336   $21.73   $21.75   $21.70  
  Purchase #4 $90.46   5.485%   $95.4217   $95.42   $95.40   $95.40  
  Purchase #5 $42.48   8.221%   $45.9723   $45.97   $45.95   $46.00  
  Purchase #6 $126.94   10.829%   $140.6863   $140.69   $140.70   $140.70  
  Purchase #7 $141.50   9.562%   $155.0302   $155.03   $155.05   $155.00  
  7 purchase totals = $636.22       $691.3524   $691.35   $691.35   $691.30