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 $224.66   9.543%   $246.0993   $246.10   $246.10   $246.10  
  Purchase #2 $147.46   6.682%   $157.3133   $157.31   $157.30   $157.30  
  Purchase #3 $24.56   7.668%   $26.4433   $26.44   $26.45   $26.40  
  Purchase #4 $84.30   12.242%   $94.62   $94.62   $94.60   $94.60  
  Purchase #5 $250.97   7.490%   $269.7677   $269.77   $269.75   $269.80  
  Purchase #6 $158.79   12.113%   $178.0242   $178.02   $178.00   $178.00  
  Purchase #7 $37.93   5.747%   $40.1098   $40.11   $40.10   $40.10  
  7 purchase totals = $928.67       $1,012.3776   $1,012.37   $1,012.30   $1,012.30