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 $166.77   9.704%   $182.9534   $182.95   $182.95   $183.00  
  Purchase #2 $154.72   12.145%   $173.5107   $173.51   $173.50   $173.50  
  Purchase #3 $188.65   9.151%   $205.9134   $205.91   $205.90   $205.90  
  Purchase #4 $24.66   6.325%   $26.2197   $26.22   $26.20   $26.20  
  Purchase #5 $236.82   4.118%   $246.5722   $246.57   $246.55   $246.60  
  Purchase #6 $129.87   9.194%   $141.8102   $141.81   $141.80   $141.80  
  Purchase #7 $137.32   9.730%   $150.6812   $150.68   $150.70   $150.70  
  7 purchase totals = $1,038.81       $1,127.6608   $1,127.65   $1,127.60   $1,127.70