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 $184.62   10.224%   $203.4955   $203.50   $203.50   $203.50  
  Purchase #2 $227.77   8.435%   $246.9824   $246.98   $247.00   $247.00  
  Purchase #3 $106.60   7.519%   $114.6153   $114.62   $114.60   $114.60  
  Purchase #4 $159.59   10.231%   $175.9177   $175.92   $175.90   $175.90  
  Purchase #5 $173.81   8.134%   $187.9477   $187.95   $187.95   $187.90  
  Purchase #6 $205.42   9.777%   $225.5039   $225.50   $225.50   $225.50  
  Purchase #7 $60.67   6.814%   $64.8041   $64.80   $64.80   $64.80  
  7 purchase totals = $1,118.48       $1,219.2666   $1,219.27   $1,219.25   $1,219.20