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 $90.67   4.808%   $95.0294   $95.03   $95.05   $95.00  
  Purchase #2 $240.67   6.393%   $256.056   $256.06   $256.05   $256.10  
  Purchase #3 $26.73   3.182%   $27.5805   $27.58   $27.60   $27.60  
  Purchase #4 $10.47   10.573%   $11.577   $11.58   $11.60   $11.60  
  Purchase #5 $9.65   4.440%   $10.0785   $10.08   $10.10   $10.10  
  Purchase #6 $230.34   10.669%   $254.915   $254.92   $254.90   $254.90  
  Purchase #7 $107.32   4.554%   $112.2074   $112.21   $112.20   $112.20  
  7 purchase totals = $715.85       $767.4438   $767.46   $767.50   $767.50