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 $73.39   3.231%   $75.7612   $75.76   $75.75   $75.80  
  Purchase #2 $208.56   9.204%   $227.7559   $227.76   $227.75   $227.80  
  Purchase #3 $29.66   3.629%   $30.7364   $30.74   $30.75   $30.70  
  Purchase #4 $130.86   9.715%   $143.573   $143.57   $143.55   $143.60  
  Purchase #5 $154.26   11.636%   $172.2097   $172.21   $172.20   $172.20  
  Purchase #6 $182.73   12.217%   $205.0541   $205.05   $205.05   $205.10  
  Purchase #7 $203.64   3.751%   $211.2785   $211.28   $211.30   $211.30  
  7 purchase totals = $983.10       $1,066.3688   $1,066.37   $1,066.35   $1,066.50