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 $106.67   10.768%   $118.1562   $118.16   $118.15   $118.20  
  Purchase #2 $153.98   13.293%   $174.4486   $174.45   $174.45   $174.40  
  Purchase #3 $134.72   6.295%   $143.2006   $143.20   $143.20   $143.20  
  Purchase #4 $78.98   10.294%   $87.1102   $87.11   $87.10   $87.10  
  Purchase #5 $75.81   13.624%   $86.1384   $86.14   $86.15   $86.10  
  Purchase #6 $179.39   6.463%   $190.984   $190.98   $191.00   $191.00  
  Purchase #7 $193.48   6.418%   $205.8975   $205.90   $205.90   $205.90  
  7 purchase totals = $923.03       $1,005.9355   $1,005.94   $1,005.95   $1,005.90