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 $111.62   4.138%   $116.2388   $116.24   $116.25   $116.20  
  Purchase #2 $194.58   3.317%   $201.0342   $201.03   $201.05   $201.00  
  Purchase #3 $205.50   12.102%   $230.3696   $230.37   $230.35   $230.40  
  Purchase #4 $67.69   4.261%   $70.5743   $70.57   $70.55   $70.60  
  Purchase #5 $51.40   8.240%   $55.6354   $55.64   $55.65   $55.60  
  Purchase #6 $135.37   10.580%   $149.6921   $149.69   $149.70   $149.70  
  Purchase #7 $186.95   9.856%   $205.3758   $205.38   $205.40   $205.40  
  7 purchase totals = $953.11       $1,028.9202   $1,028.92   $1,028.95   $1,028.90