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 $63.86   4.700%   $66.8614   $66.86   $66.85   $66.90  
  Purchase #2 $192.75   13.453%   $218.6807   $218.68   $218.70   $218.70  
  Purchase #3 $172.69   12.301%   $193.9326   $193.93   $193.95   $193.90  
  Purchase #4 $136.34   12.643%   $153.5775   $153.58   $153.60   $153.60  
  Purchase #5 $235.46   9.863%   $258.6834   $258.68   $258.70   $258.70  
  Purchase #6 $176.26   10.529%   $194.8184   $194.82   $194.80   $194.80  
  Purchase #7 $6.33   10.780%   $7.0124   $7.01   $7.00   $7.00  
  7 purchase totals = $983.69       $1,093.5664   $1,093.56   $1,093.60   $1,093.60