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 $66.25   13.203%   $74.997   $75.00   $75.00   $75.00  
  Purchase #2 $181.55   8.417%   $196.8311   $196.83   $196.85   $196.80  
  Purchase #3 $189.49   4.215%   $197.477   $197.48   $197.50   $197.50  
  Purchase #4 $66.47   12.466%   $74.7562   $74.76   $74.75   $74.80  
  Purchase #5 $142.70   9.786%   $156.6646   $156.66   $156.65   $156.70  
  Purchase #6 $227.44   8.614%   $247.0317   $247.03   $247.05   $247.00  
  Purchase #7 $27.31   5.447%   $28.7976   $28.80   $28.80   $28.80  
  7 purchase totals = $901.21       $976.5552   $976.56   $976.60   $976.60