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 $196.56   13.629%   $223.3492   $223.35   $223.35   $223.30  
  Purchase #2 $190.84   7.128%   $204.4431   $204.44   $204.45   $204.40  
  Purchase #3 $233.58   8.352%   $253.0886   $253.09   $253.10   $253.10  
  Purchase #4 $154.25   7.789%   $166.2645   $166.26   $166.25   $166.30  
  Purchase #5 $171.33   8.705%   $186.2443   $186.24   $186.25   $186.20  
  Purchase #6 $250.87   8.229%   $271.5141   $271.51   $271.50   $271.50  
  Purchase #7 $52.98   9.516%   $58.0216   $58.02   $58.00   $58.00  
  7 purchase totals = $1,250.41       $1,362.9254   $1,362.91   $1,362.90   $1,362.80