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 $62.61   4.716%   $65.5627   $65.56   $65.55   $65.60  
  Purchase #2 $233.84   7.433%   $251.2213   $251.22   $251.20   $251.20  
  Purchase #3 $34.81   6.226%   $36.9773   $36.98   $37.00   $37.00  
  Purchase #4 $226.48   5.604%   $239.1719   $239.17   $239.15   $239.20  
  Purchase #5 $240.32   5.175%   $252.7566   $252.76   $252.75   $252.80  
  Purchase #6 $130.79   7.616%   $140.751   $140.75   $140.75   $140.80  
  Purchase #7 $128.37   11.560%   $143.2096   $143.21   $143.20   $143.20  
  7 purchase totals = $1,057.22       $1,129.6504   $1,129.65   $1,129.60   $1,129.80