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 $236.31   7.734%   $254.5862   $254.59   $254.60   $254.60  
  Purchase #2 $246.35   11.218%   $273.9855   $273.99   $274.00   $274.00  
  Purchase #3 $70.70   8.269%   $76.5462   $76.55   $76.55   $76.50  
  Purchase #4 $122.89   3.493%   $127.1825   $127.18   $127.20   $127.20  
  Purchase #5 $83.58   4.719%   $87.5241   $87.52   $87.50   $87.50  
  Purchase #6 $176.72   4.110%   $183.9832   $183.98   $184.00   $184.00  
  Purchase #7 $150.59   6.692%   $160.6675   $160.67   $160.65   $160.70  
  7 purchase totals = $1,087.14       $1,164.4752   $1,164.48   $1,164.50   $1,164.50