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 $177.95   9.649%   $195.1204   $195.12   $195.10   $195.10  
  Purchase #2 $234.43   12.788%   $264.4089   $264.41   $264.40   $264.40  
  Purchase #3 $238.38   5.447%   $251.3646   $251.36   $251.35   $251.40  
  Purchase #4 $73.91   8.310%   $80.0519   $80.05   $80.05   $80.10  
  Purchase #5 $52.86   10.749%   $58.5419   $58.54   $58.55   $58.50  
  Purchase #6 $247.47   10.240%   $272.8109   $272.81   $272.80   $272.80  
  Purchase #7 $116.94   11.470%   $130.353   $130.35   $130.35   $130.40  
  7 purchase totals = $1,141.94       $1,252.6516   $1,252.64   $1,252.60   $1,252.70