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 $244.72   8.112%   $264.5717   $264.57   $264.55   $264.60  
  Purchase #2 $239.46   10.670%   $265.0104   $265.01   $265.00   $265.00  
  Purchase #3 $115.98   8.203%   $125.4938   $125.49   $125.50   $125.50  
  Purchase #4 $111.71   10.154%   $123.053   $123.05   $123.05   $123.10  
  Purchase #5 $177.81   3.604%   $184.2183   $184.22   $184.20   $184.20  
  Purchase #6 $167.69   3.797%   $174.0572   $174.06   $174.05   $174.10  
  Purchase #7 $11.89   3.681%   $12.3277   $12.33   $12.35   $12.30  
  7 purchase totals = $1,069.26       $1,148.7321   $1,148.73   $1,148.70   $1,148.80