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 $63.67   7.144%   $68.2186   $68.22   $68.20   $68.20  
  Purchase #2 $208.86   9.303%   $228.2902   $228.29   $228.30   $228.30  
  Purchase #3 $202.92   4.315%   $211.676   $211.68   $211.70   $211.70  
  Purchase #4 $33.59   4.313%   $35.0387   $35.04   $35.05   $35.00  
  Purchase #5 $246.73   5.165%   $259.4736   $259.47   $259.45   $259.50  
  Purchase #6 $95.81   3.313%   $98.9842   $98.98   $99.00   $99.00  
  Purchase #7 $18.76   13.827%   $21.3539   $21.35   $21.35   $21.40  
  7 purchase totals = $870.34       $923.0352   $923.03   $923.05   $923.10