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 $84.99   11.230%   $94.5344   $94.53   $94.55   $94.50  
  Purchase #2 $152.72   3.412%   $157.9308   $157.93   $157.95   $157.90  
  Purchase #3 $5.66   6.492%   $6.0274   $6.03   $6.05   $6.00  
  Purchase #4 $56.96   3.265%   $58.8197   $58.82   $58.80   $58.80  
  Purchase #5 $181.40   11.249%   $201.8057   $201.81   $201.80   $201.80  
  Purchase #6 $214.95   11.256%   $239.1448   $239.14   $239.15   $239.10  
  Purchase #7 $192.64   10.531%   $212.9269   $212.93   $212.95   $212.90  
  7 purchase totals = $889.32       $971.1897   $971.19   $971.25   $971.00