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 $91.31   11.551%   $101.8572   $101.86   $101.85   $101.90  
  Purchase #2 $206.29   13.457%   $234.0504   $234.05   $234.05   $234.10  
  Purchase #3 $177.26   6.306%   $188.438   $188.44   $188.45   $188.40  
  Purchase #4 $173.57   11.511%   $193.5496   $193.55   $193.55   $193.50  
  Purchase #5 $35.31   12.183%   $39.6118   $39.61   $39.60   $39.60  
  Purchase #6 $6.36   13.481%   $7.2174   $7.22   $7.20   $7.20  
  Purchase #7 $219.97   12.235%   $246.8833   $246.88   $246.90   $246.90  
  7 purchase totals = $910.07       $1,011.6077   $1,011.61   $1,011.60   $1,011.60