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 $204.99   10.757%   $227.0408   $227.04   $227.05   $227.00  
  Purchase #2 $62.80   4.843%   $65.8414   $65.84   $65.85   $65.80  
  Purchase #3 $182.86   5.749%   $193.3726   $193.37   $193.35   $193.40  
  Purchase #4 $50.39   12.635%   $56.7568   $56.76   $56.75   $56.80  
  Purchase #5 $222.70   9.151%   $243.0793   $243.08   $243.10   $243.10  
  Purchase #6 $98.91   4.496%   $103.357   $103.36   $103.35   $103.40  
  Purchase #7 $13.71   5.791%   $14.5039   $14.50   $14.50   $14.50  
  7 purchase totals = $836.36       $903.9518   $903.95   $903.95   $904.00