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 $70.43   3.861%   $73.1493   $73.15   $73.15   $73.10  
  Purchase #2 $50.53   12.245%   $56.7174   $56.72   $56.70   $56.70  
  Purchase #3 $248.67   3.556%   $257.5127   $257.51   $257.50   $257.50  
  Purchase #4 $143.80   5.170%   $151.2345   $151.23   $151.25   $151.20  
  Purchase #5 $204.35   11.426%   $227.699   $227.70   $227.70   $227.70  
  Purchase #6 $207.86   3.785%   $215.7275   $215.73   $215.75   $215.70  
  Purchase #7 $24.43   4.297%   $25.4798   $25.48   $25.50   $25.50  
  7 purchase totals = $950.07       $1,007.5202   $1,007.52   $1,007.55   $1,007.40