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 $231.68   6.355%   $246.4033   $246.40   $246.40   $246.40  
  Purchase #2 $128.81   9.637%   $141.2234   $141.22   $141.20   $141.20  
  Purchase #3 $59.54   6.246%   $63.2589   $63.26   $63.25   $63.30  
  Purchase #4 $184.39   5.717%   $194.9316   $194.93   $194.95   $194.90  
  Purchase #5 $5.26   12.319%   $5.908   $5.91   $5.90   $5.90  
  Purchase #6 $240.28   13.766%   $273.3569   $273.36   $273.35   $273.40  
  Purchase #7 $122.88   5.306%   $129.4   $129.40   $129.40   $129.40  
  7 purchase totals = $972.84       $1,054.4821   $1,054.48   $1,054.45   $1,054.50