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 $146.87   4.416%   $153.3558   $153.36   $153.35   $153.40  
  Purchase #2 $152.53   6.530%   $162.4902   $162.49   $162.50   $162.50  
  Purchase #3 $211.96   3.591%   $219.5715   $219.57   $219.55   $219.60  
  Purchase #4 $221.47   3.388%   $228.9734   $228.97   $228.95   $229.00  
  Purchase #5 $226.81   5.813%   $239.9945   $239.99   $240.00   $240.00  
  Purchase #6 $46.36   8.519%   $50.3094   $50.31   $50.30   $50.30  
  Purchase #7 $71.97   4.134%   $74.9452   $74.95   $74.95   $74.90  
  7 purchase totals = $1,077.97       $1,129.6400   $1,129.64   $1,129.60   $1,129.70