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 $69.84   6.386%   $74.3   $74.30   $74.30   $74.30  
  Purchase #2 $169.48   11.230%   $188.5126   $188.51   $188.50   $188.50  
  Purchase #3 $198.53   13.510%   $225.3514   $225.35   $225.35   $225.40  
  Purchase #4 $53.59   4.843%   $56.1854   $56.19   $56.20   $56.20  
  Purchase #5 $240.71   12.157%   $269.9731   $269.97   $269.95   $270.00  
  Purchase #6 $65.29   9.712%   $71.631   $71.63   $71.65   $71.60  
  Purchase #7 $119.88   4.754%   $125.5791   $125.58   $125.60   $125.60  
  7 purchase totals = $917.32       $1,011.5326   $1,011.53   $1,011.55   $1,011.60