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 $38.43   13.451%   $43.5992   $43.60   $43.60   $43.60  
  Purchase #2 $128.88   6.507%   $137.2662   $137.27   $137.25   $137.30  
  Purchase #3 $57.59   12.468%   $64.7703   $64.77   $64.75   $64.80  
  Purchase #4 $222.98   5.402%   $235.0254   $235.03   $235.05   $235.00  
  Purchase #5 $59.73   3.479%   $61.808   $61.81   $61.80   $61.80  
  Purchase #6 $230.69   13.136%   $260.9934   $260.99   $261.00   $261.00  
  Purchase #7 $202.81   8.327%   $219.698   $219.70   $219.70   $219.70  
  7 purchase totals = $941.11       $1,023.1605   $1,023.17   $1,023.15   $1,023.20