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 $16.30   8.592%   $17.7005   $17.70   $17.70   $17.70  
  Purchase #2 $177.79   7.158%   $190.5162   $190.52   $190.50   $190.50  
  Purchase #3 $48.83   8.581%   $53.0201   $53.02   $53.00   $53.00  
  Purchase #4 $101.43   12.235%   $113.84   $113.84   $113.85   $113.80  
  Purchase #5 $153.33   9.570%   $168.0037   $168.00   $168.00   $168.00  
  Purchase #6 $214.77   4.761%   $224.9952   $225.00   $225.00   $225.00  
  Purchase #7 $75.56   5.621%   $79.8072   $79.81   $79.80   $79.80  
  7 purchase totals = $788.01       $847.8829   $847.89   $847.85   $847.80