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 $58.50   12.834%   $66.0079   $66.01   $66.00   $66.00  
  Purchase #2 $224.96   5.181%   $236.6152   $236.62   $236.60   $236.60  
  Purchase #3 $155.46   7.144%   $166.5661   $166.57   $166.55   $166.60  
  Purchase #4 $131.26   12.169%   $147.233   $147.23   $147.25   $147.20  
  Purchase #5 $188.78   5.582%   $199.3177   $199.32   $199.30   $199.30  
  Purchase #6 $173.33   8.575%   $188.193   $188.19   $188.20   $188.20  
  Purchase #7 $204.36   12.575%   $230.0583   $230.06   $230.05   $230.10  
  7 purchase totals = $1,136.65       $1,233.9912   $1,234.00   $1,233.95   $1,234.00