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 $89.38   13.640%   $101.5714   $101.57   $101.55   $101.60  
  Purchase #2 $219.81   6.298%   $233.6536   $233.65   $233.65   $233.70  
  Purchase #3 $222.60   8.355%   $241.1982   $241.20   $241.20   $241.20  
  Purchase #4 $195.35   11.635%   $218.079   $218.08   $218.10   $218.10  
  Purchase #5 $222.79   10.581%   $246.3634   $246.36   $246.35   $246.40  
  Purchase #6 $228.44   8.331%   $247.4713   $247.47   $247.45   $247.50  
  Purchase #7 $31.99   7.221%   $34.3   $34.30   $34.30   $34.30  
  7 purchase totals = $1,210.36       $1,322.6369   $1,322.63   $1,322.60   $1,322.80