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 $242.61   9.722%   $266.1965   $266.20   $266.20   $266.20  
  Purchase #2 $138.66   10.342%   $153.0002   $153.00   $153.00   $153.00  
  Purchase #3 $122.55   8.317%   $132.7425   $132.74   $132.75   $132.70  
  Purchase #4 $108.52   6.843%   $115.946   $115.95   $115.95   $115.90  
  Purchase #5 $175.39   5.130%   $184.3875   $184.39   $184.40   $184.40  
  Purchase #6 $204.74   7.727%   $220.5603   $220.56   $220.55   $220.60  
  Purchase #7 $147.92   3.817%   $153.5661   $153.57   $153.55   $153.60  
  7 purchase totals = $1,140.39       $1,226.3991   $1,226.41   $1,226.40   $1,226.40