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 $247.25   10.832%   $274.0321   $274.03   $274.05   $274.00  
  Purchase #2 $211.58   4.117%   $220.2907   $220.29   $220.30   $220.30  
  Purchase #3 $117.93   3.169%   $121.6672   $121.67   $121.65   $121.70  
  Purchase #4 $19.78   10.747%   $21.9058   $21.91   $21.90   $21.90  
  Purchase #5 $124.67   5.204%   $131.1578   $131.16   $131.15   $131.20  
  Purchase #6 $41.50   10.634%   $45.9131   $45.91   $45.90   $45.90  
  Purchase #7 $208.96   8.258%   $226.2159   $226.22   $226.20   $226.20  
  7 purchase totals = $971.67       $1,041.1826   $1,041.19   $1,041.15   $1,041.20