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 $85.77   12.484%   $96.4775   $96.48   $96.50   $96.50  
  Purchase #2 $127.87   12.314%   $143.6159   $143.62   $143.60   $143.60  
  Purchase #3 $191.40   4.501%   $200.0149   $200.01   $200.00   $200.00  
  Purchase #4 $55.30   11.676%   $61.7568   $61.76   $61.75   $61.80  
  Purchase #5 $239.97   8.194%   $259.6331   $259.63   $259.65   $259.60  
  Purchase #6 $229.97   3.642%   $238.3455   $238.35   $238.35   $238.30  
  Purchase #7 $23.88   12.131%   $26.7769   $26.78   $26.80   $26.80  
  7 purchase totals = $954.16       $1,026.6206   $1,026.63   $1,026.65   $1,026.60