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 $61.88   3.774%   $64.2154   $64.22   $64.20   $64.20  
  Purchase #2 $172.46   8.835%   $187.6968   $187.70   $187.70   $187.70  
  Purchase #3 $227.59   13.549%   $258.4262   $258.43   $258.45   $258.40  
  Purchase #4 $95.51   8.466%   $103.5959   $103.60   $103.60   $103.60  
  Purchase #5 $10.33   4.160%   $10.7597   $10.76   $10.75   $10.80  
  Purchase #6 $203.91   11.204%   $226.7561   $226.76   $226.75   $226.80  
  Purchase #7 $126.65   6.561%   $134.9595   $134.96   $134.95   $135.00  
  7 purchase totals = $898.33       $986.4096   $986.43   $986.40   $986.50