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 $208.48   13.426%   $236.4705   $236.47   $236.45   $236.50  
  Purchase #2 $190.63   10.700%   $211.0274   $211.03   $211.05   $211.00  
  Purchase #3 $94.93   7.168%   $101.7346   $101.73   $101.75   $101.70  
  Purchase #4 $181.57   5.809%   $192.1174   $192.12   $192.10   $192.10  
  Purchase #5 $9.85   6.808%   $10.5206   $10.52   $10.50   $10.50  
  Purchase #6 $160.50   8.347%   $173.8969   $173.90   $173.90   $173.90  
  Purchase #7 $236.54   13.532%   $268.5486   $268.55   $268.55   $268.50  
  7 purchase totals = $1,082.50       $1,194.3160   $1,194.32   $1,194.30   $1,194.20