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 $67.59   8.278%   $73.1851   $73.19   $73.20   $73.20  
  Purchase #2 $141.82   9.654%   $155.5113   $155.51   $155.50   $155.50  
  Purchase #3 $168.46   12.609%   $189.7011   $189.70   $189.70   $189.70  
  Purchase #4 $235.89   5.216%   $248.194   $248.19   $248.20   $248.20  
  Purchase #5 $122.58   7.425%   $131.6816   $131.68   $131.70   $131.70  
  Purchase #6 $116.94   12.604%   $131.6791   $131.68   $131.70   $131.70  
  Purchase #7 $116.66   3.236%   $120.4351   $120.44   $120.45   $120.40  
  7 purchase totals = $969.94       $1,050.3873   $1,050.39   $1,050.45   $1,050.40