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 $226.91   8.189%   $245.4917   $245.49   $245.50   $245.50  
  Purchase #2 $32.88   9.763%   $36.0901   $36.09   $36.10   $36.10  
  Purchase #3 $152.41   9.624%   $167.0779   $167.08   $167.10   $167.10  
  Purchase #4 $62.59   12.182%   $70.2147   $70.21   $70.20   $70.20  
  Purchase #5 $247.39   6.531%   $263.547   $263.55   $263.55   $263.50  
  Purchase #6 $59.88   4.408%   $62.5195   $62.52   $62.50   $62.50  
  Purchase #7 $178.65   5.470%   $188.4222   $188.42   $188.40   $188.40  
  7 purchase totals = $960.71       $1,033.3631   $1,033.36   $1,033.35   $1,033.30