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 $63.84   12.106%   $71.5685   $71.57   $71.55   $71.60  
  Purchase #2 $168.97   8.302%   $182.9979   $183.00   $183.00   $183.00  
  Purchase #3 $164.25   7.504%   $176.5753   $176.58   $176.60   $176.60  
  Purchase #4 $23.75   6.622%   $25.3227   $25.32   $25.30   $25.30  
  Purchase #5 $245.26   9.584%   $268.7657   $268.77   $268.75   $268.80  
  Purchase #6 $193.60   13.444%   $219.6276   $219.63   $219.65   $219.60  
  Purchase #7 $219.26   6.712%   $233.9767   $233.98   $234.00   $234.00  
  7 purchase totals = $1,078.93       $1,178.8344   $1,178.85   $1,178.85   $1,178.90