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 $120.39   3.848%   $125.0226   $125.02   $125.00   $125.00  
  Purchase #2 $198.47   7.362%   $213.0814   $213.08   $213.10   $213.10  
  Purchase #3 $87.43   7.139%   $93.6716   $93.67   $93.65   $93.70  
  Purchase #4 $209.94   8.236%   $227.2307   $227.23   $227.25   $227.20  
  Purchase #5 $237.52   10.350%   $262.1033   $262.10   $262.10   $262.10  
  Purchase #6 $23.70   13.752%   $26.9592   $26.96   $26.95   $27.00  
  Purchase #7 $62.94   10.374%   $69.4694   $69.47   $69.45   $69.50  
  7 purchase totals = $940.39       $1,017.5382   $1,017.53   $1,017.50   $1,017.60