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 $60.57   13.621%   $68.8202   $68.82   $68.80   $68.80  
  Purchase #2 $209.32   13.871%   $238.3548   $238.35   $238.35   $238.40  
  Purchase #3 $134.84   12.551%   $151.7638   $151.76   $151.75   $151.80  
  Purchase #4 $56.65   6.668%   $60.4274   $60.43   $60.45   $60.40  
  Purchase #5 $221.46   6.424%   $235.6866   $235.69   $235.70   $235.70  
  Purchase #6 $148.59   3.275%   $153.4563   $153.46   $153.45   $153.50  
  Purchase #7 $214.81   4.422%   $224.3089   $224.31   $224.30   $224.30  
  7 purchase totals = $1,046.24       $1,132.8180   $1,132.82   $1,132.80   $1,132.90