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 $51.56   11.618%   $57.5502   $57.55   $57.55   $57.60  
  Purchase #2 $228.25   12.470%   $256.7128   $256.71   $256.70   $256.70  
  Purchase #3 $241.71   4.668%   $252.993   $252.99   $253.00   $253.00  
  Purchase #4 $191.27   4.213%   $199.3282   $199.33   $199.35   $199.30  
  Purchase #5 $235.36   12.732%   $265.326   $265.33   $265.35   $265.30  
  Purchase #6 $149.83   8.663%   $162.8098   $162.81   $162.80   $162.80  
  Purchase #7 $43.72   6.203%   $46.432   $46.43   $46.45   $46.40  
  7 purchase totals = $1,141.70       $1,241.1520   $1,241.15   $1,241.20   $1,241.10