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 $95.58   10.867%   $105.9667   $105.97   $105.95   $106.00  
  Purchase #2 $226.88   10.440%   $250.5663   $250.57   $250.55   $250.60  
  Purchase #3 $128.95   7.764%   $138.9617   $138.96   $138.95   $139.00  
  Purchase #4 $131.43   13.353%   $148.9798   $148.98   $149.00   $149.00  
  Purchase #5 $61.43   6.646%   $65.5126   $65.51   $65.50   $65.50  
  Purchase #6 $201.92   12.207%   $226.5684   $226.57   $226.55   $226.60  
  Purchase #7 $193.50   10.472%   $213.7633   $213.76   $213.75   $213.80  
  7 purchase totals = $1,039.69       $1,150.3188   $1,150.32   $1,150.25   $1,150.50