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 $56.90   8.258%   $61.5988   $61.60   $61.60   $61.60  
  Purchase #2 $226.87   8.443%   $246.0246   $246.02   $246.00   $246.00  
  Purchase #3 $204.46   10.373%   $225.6686   $225.67   $225.65   $225.70  
  Purchase #4 $14.42   13.744%   $16.4019   $16.40   $16.40   $16.40  
  Purchase #5 $169.66   10.646%   $187.722   $187.72   $187.70   $187.70  
  Purchase #6 $241.31   6.681%   $257.4319   $257.43   $257.45   $257.40  
  Purchase #7 $123.35   9.804%   $135.4432   $135.44   $135.45   $135.40  
  7 purchase totals = $1,036.97       $1,130.2910   $1,130.28   $1,130.25   $1,130.20