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 $33.93   7.812%   $36.5806   $36.58   $36.60   $36.60  
  Purchase #2 $162.96   8.852%   $177.3852   $177.39   $177.40   $177.40  
  Purchase #3 $33.82   5.601%   $35.7143   $35.71   $35.70   $35.70  
  Purchase #4 $206.68   6.675%   $220.4759   $220.48   $220.50   $220.50  
  Purchase #5 $91.89   4.487%   $96.0131   $96.01   $96.00   $96.00  
  Purchase #6 $240.31   12.746%   $270.9399   $270.94   $270.95   $270.90  
  Purchase #7 $109.58   6.386%   $116.5778   $116.58   $116.60   $116.60  
  7 purchase totals = $879.17       $953.6868   $953.69   $953.75   $953.70