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 $231.25   9.104%   $252.303   $252.30   $252.30   $252.30  
  Purchase #2 $222.28   10.835%   $246.364   $246.36   $246.35   $246.40  
  Purchase #3 $142.58   7.702%   $153.5615   $153.56   $153.55   $153.60  
  Purchase #4 $96.35   3.535%   $99.756   $99.76   $99.75   $99.80  
  Purchase #5 $108.90   11.582%   $121.5128   $121.51   $121.50   $121.50  
  Purchase #6 $139.64   8.611%   $151.6644   $151.66   $151.65   $151.70  
  Purchase #7 $20.73   10.643%   $22.9363   $22.94   $22.95   $22.90  
  7 purchase totals = $961.73       $1,048.0980   $1,048.09   $1,048.05   $1,048.20