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 $53.94   6.766%   $57.5896   $57.59   $57.60   $57.60  
  Purchase #2 $61.69   9.148%   $67.3334   $67.33   $67.35   $67.30  
  Purchase #3 $166.34   3.852%   $172.7474   $172.75   $172.75   $172.70  
  Purchase #4 $208.46   9.399%   $228.0532   $228.05   $228.05   $228.10  
  Purchase #5 $99.84   6.643%   $106.4724   $106.47   $106.45   $106.50  
  Purchase #6 $122.45   6.618%   $130.5537   $130.55   $130.55   $130.60  
  Purchase #7 $19.35   13.873%   $22.0344   $22.03   $22.05   $22.00  
  7 purchase totals = $732.07       $784.7841   $784.77   $784.80   $784.80