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 $47.26   12.202%   $53.0267   $53.03   $53.05   $53.00  
  Purchase #2 $163.92   10.541%   $181.1988   $181.20   $181.20   $181.20  
  Purchase #3 $164.87   5.459%   $173.8703   $173.87   $173.85   $173.90  
  Purchase #4 $92.32   12.639%   $103.9883   $103.99   $104.00   $104.00  
  Purchase #5 $141.69   5.175%   $149.0225   $149.02   $149.00   $149.00  
  Purchase #6 $62.42   9.257%   $68.1982   $68.20   $68.20   $68.20  
  Purchase #7 $39.43   5.710%   $41.6815   $41.68   $41.70   $41.70  
  7 purchase totals = $711.91       $770.9863   $770.99   $771.00   $771.00