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 $163.61   9.111%   $178.5165   $178.52   $178.50   $178.50  
  Purchase #2 $78.83   3.453%   $81.552   $81.55   $81.55   $81.60  
  Purchase #3 $241.50   4.493%   $252.3506   $252.35   $252.35   $252.40  
  Purchase #4 $71.63   3.404%   $74.0683   $74.07   $74.05   $74.10  
  Purchase #5 $110.27   6.212%   $117.12   $117.12   $117.10   $117.10  
  Purchase #6 $241.30   10.543%   $266.7403   $266.74   $266.75   $266.70  
  Purchase #7 $53.46   4.497%   $55.8641   $55.86   $55.85   $55.90  
  7 purchase totals = $960.60       $1,026.2118   $1,026.21   $1,026.15   $1,026.30