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 $60.58   10.627%   $67.0178   $67.02   $67.00   $67.00  
  Purchase #2 $250.67   10.335%   $276.5767   $276.58   $276.60   $276.60  
  Purchase #3 $247.81   8.802%   $269.6222   $269.62   $269.60   $269.60  
  Purchase #4 $141.96   11.772%   $158.6715   $158.67   $158.65   $158.70  
  Purchase #5 $35.29   7.706%   $38.0094   $38.01   $38.00   $38.00  
  Purchase #6 $87.67   9.723%   $96.1942   $96.19   $96.20   $96.20  
  Purchase #7 $164.74   6.651%   $175.6969   $175.70   $175.70   $175.70  
  7 purchase totals = $988.72       $1,081.7887   $1,081.79   $1,081.75   $1,081.80