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 $208.67   11.714%   $233.1136   $233.11   $233.10   $233.10  
  Purchase #2 $160.71   12.224%   $180.3552   $180.36   $180.35   $180.40  
  Purchase #3 $104.49   10.685%   $115.6548   $115.65   $115.65   $115.70  
  Purchase #4 $229.37   9.482%   $251.1189   $251.12   $251.10   $251.10  
  Purchase #5 $122.87   8.870%   $133.7686   $133.77   $133.75   $133.80  
  Purchase #6 $67.53   12.544%   $76.001   $76.00   $76.00   $76.00  
  Purchase #7 $5.54   12.174%   $6.2144   $6.21   $6.20   $6.20  
  7 purchase totals = $899.18       $996.2265   $996.22   $996.15   $996.30