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 $226.88   8.415%   $245.972   $245.97   $245.95   $246.00  
  Purchase #2 $214.46   11.367%   $238.8377   $238.84   $238.85   $238.80  
  Purchase #3 $45.88   11.437%   $51.1273   $51.13   $51.15   $51.10  
  Purchase #4 $89.29   10.741%   $98.8806   $98.88   $98.90   $98.90  
  Purchase #5 $213.83   8.301%   $231.58   $231.58   $231.60   $231.60  
  Purchase #6 $149.92   5.416%   $158.0397   $158.04   $158.05   $158.00  
  Purchase #7 $9.58   5.548%   $10.1115   $10.11   $10.10   $10.10  
  7 purchase totals = $949.84       $1,034.5488   $1,034.55   $1,034.60   $1,034.50