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 $58.34   12.549%   $65.6611   $65.66   $65.65   $65.70  
  Purchase #2 $116.97   7.352%   $125.5696   $125.57   $125.55   $125.60  
  Purchase #3 $161.51   7.833%   $174.1611   $174.16   $174.15   $174.20  
  Purchase #4 $18.84   3.525%   $19.5041   $19.50   $19.50   $19.50  
  Purchase #5 $208.93   11.345%   $232.6331   $232.63   $232.65   $232.60  
  Purchase #6 $117.61   6.685%   $125.4722   $125.47   $125.45   $125.50  
  Purchase #7 $166.74   6.381%   $177.3797   $177.38   $177.40   $177.40  
  7 purchase totals = $848.94       $920.3809   $920.37   $920.35   $920.50