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 $119.68   13.713%   $136.0917   $136.09   $136.10   $136.10  
  Purchase #2 $41.52   13.687%   $47.2028   $47.20   $47.20   $47.20  
  Purchase #3 $197.35   13.558%   $224.1067   $224.11   $224.10   $224.10  
  Purchase #4 $231.43   12.189%   $259.639   $259.64   $259.65   $259.60  
  Purchase #5 $219.71   9.726%   $241.079   $241.08   $241.10   $241.10  
  Purchase #6 $53.37   13.266%   $60.4501   $60.45   $60.45   $60.50  
  Purchase #7 $197.40   12.661%   $222.3928   $222.39   $222.40   $222.40  
  7 purchase totals = $1,060.46       $1,190.9621   $1,190.96   $1,191.00   $1,191.00