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 $204.63   10.483%   $226.0814   $226.08   $226.10   $226.10  
  Purchase #2 $100.95   9.383%   $110.4221   $110.42   $110.40   $110.40  
  Purchase #3 $65.94   10.681%   $72.9831   $72.98   $73.00   $73.00  
  Purchase #4 $234.44   12.106%   $262.8213   $262.82   $262.80   $262.80  
  Purchase #5 $223.52   13.628%   $253.9813   $253.98   $254.00   $254.00  
  Purchase #6 $69.60   6.536%   $74.1491   $74.15   $74.15   $74.10  
  Purchase #7 $162.25   8.489%   $176.0234   $176.02   $176.00   $176.00  
  7 purchase totals = $1,061.33       $1,176.4617   $1,176.45   $1,176.45   $1,176.40