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 $185.92   10.314%   $205.0958   $205.10   $205.10   $205.10  
  Purchase #2 $204.57   11.280%   $227.6455   $227.65   $227.65   $227.60  
  Purchase #3 $21.63   11.568%   $24.1322   $24.13   $24.15   $24.10  
  Purchase #4 $247.51   5.807%   $261.8829   $261.88   $261.90   $261.90  
  Purchase #5 $129.52   9.448%   $141.757   $141.76   $141.75   $141.80  
  Purchase #6 $86.74   11.353%   $96.5876   $96.59   $96.60   $96.60  
  Purchase #7 $137.88   12.551%   $155.1853   $155.19   $155.20   $155.20  
  7 purchase totals = $1,013.77       $1,112.2863   $1,112.30   $1,112.35   $1,112.30