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 $67.29   10.811%   $74.5647   $74.56   $74.55   $74.60  
  Purchase #2 $217.75   4.234%   $226.9695   $226.97   $226.95   $227.00  
  Purchase #3 $120.35   10.270%   $132.7099   $132.71   $132.70   $132.70  
  Purchase #4 $29.85   4.659%   $31.2407   $31.24   $31.25   $31.20  
  Purchase #5 $166.61   10.688%   $184.4173   $184.42   $184.40   $184.40  
  Purchase #6 $39.26   4.243%   $40.9258   $40.93   $40.95   $40.90  
  Purchase #7 $230.29   11.669%   $257.1625   $257.16   $257.15   $257.20  
  7 purchase totals = $871.40       $947.9904   $947.99   $947.95   $948.00