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 $191.82   5.364%   $202.1092   $202.11   $202.10   $202.10  
  Purchase #2 $52.80   11.623%   $58.9369   $58.94   $58.95   $58.90  
  Purchase #3 $53.64   5.527%   $56.6047   $56.60   $56.60   $56.60  
  Purchase #4 $55.71   8.345%   $60.359   $60.36   $60.35   $60.40  
  Purchase #5 $35.42   12.273%   $39.7671   $39.77   $39.75   $39.80  
  Purchase #6 $110.87   3.707%   $114.98   $114.98   $115.00   $115.00  
  Purchase #7 $67.28   4.697%   $70.4401   $70.44   $70.45   $70.40  
  7 purchase totals = $567.54       $603.1970   $603.20   $603.20   $603.20