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 $157.89   10.583%   $174.5995   $174.60   $174.60   $174.60  
  Purchase #2 $229.25   5.432%   $241.7029   $241.70   $241.70   $241.70  
  Purchase #3 $246.39   7.364%   $264.5342   $264.53   $264.55   $264.50  
  Purchase #4 $212.26   3.412%   $219.5023   $219.50   $219.50   $219.50  
  Purchase #5 $121.81   6.684%   $129.9518   $129.95   $129.95   $130.00  
  Purchase #6 $19.57   8.832%   $21.2984   $21.30   $21.30   $21.30  
  Purchase #7 $109.32   12.654%   $123.1534   $123.15   $123.15   $123.20  
  7 purchase totals = $1,096.49       $1,174.7425   $1,174.73   $1,174.75   $1,174.80