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 $82.65   6.430%   $87.9644   $87.96   $87.95   $88.00  
  Purchase #2 $178.41   6.729%   $190.4152   $190.42   $190.40   $190.40  
  Purchase #3 $11.33   7.651%   $12.1969   $12.20   $12.20   $12.20  
  Purchase #4 $46.61   6.174%   $49.4877   $49.49   $49.50   $49.50  
  Purchase #5 $208.55   11.402%   $232.3289   $232.33   $232.35   $232.30  
  Purchase #6 $106.68   6.527%   $113.643   $113.64   $113.65   $113.60  
  Purchase #7 $176.31   5.162%   $185.4111   $185.41   $185.40   $185.40  
  7 purchase totals = $810.54       $871.4472   $871.45   $871.45   $871.40