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 $188.57   12.319%   $211.7999   $211.80   $211.80   $211.80  
  Purchase #2 $35.70   4.378%   $37.2629   $37.26   $37.25   $37.30  
  Purchase #3 $154.68   13.475%   $175.5231   $175.52   $175.50   $175.50  
  Purchase #4 $207.41   4.301%   $216.3307   $216.33   $216.35   $216.30  
  Purchase #5 $78.51   3.407%   $81.1848   $81.18   $81.20   $81.20  
  Purchase #6 $219.68   9.834%   $241.2833   $241.28   $241.30   $241.30  
  Purchase #7 $231.91   13.165%   $262.441   $262.44   $262.45   $262.40  
  7 purchase totals = $1,116.46       $1,225.8257   $1,225.81   $1,225.85   $1,225.80