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 $212.75   12.724%   $239.8203   $239.82   $239.80   $239.80  
  Purchase #2 $33.39   5.771%   $35.3169   $35.32   $35.30   $35.30  
  Purchase #3 $212.67   13.496%   $241.3719   $241.37   $241.35   $241.40  
  Purchase #4 $51.43   7.435%   $55.2538   $55.25   $55.25   $55.30  
  Purchase #5 $225.33   12.559%   $253.6292   $253.63   $253.65   $253.60  
  Purchase #6 $66.71   3.263%   $68.8867   $68.89   $68.90   $68.90  
  Purchase #7 $131.91   4.830%   $138.2813   $138.28   $138.30   $138.30  
  7 purchase totals = $934.19       $1,032.5601   $1,032.56   $1,032.55   $1,032.60