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 $24.65   7.849%   $26.5848   $26.58   $26.60   $26.60  
  Purchase #2 $82.67   10.286%   $91.1734   $91.17   $91.15   $91.20  
  Purchase #3 $140.61   3.497%   $145.5271   $145.53   $145.55   $145.50  
  Purchase #4 $201.32   4.274%   $209.9244   $209.92   $209.90   $209.90  
  Purchase #5 $219.70   12.148%   $246.3892   $246.39   $246.40   $246.40  
  Purchase #6 $234.29   8.313%   $253.7665   $253.77   $253.75   $253.80  
  Purchase #7 $70.78   5.838%   $74.9121   $74.91   $74.90   $74.90  
  7 purchase totals = $974.02       $1,048.2775   $1,048.27   $1,048.25   $1,048.30