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 $33.58   11.710%   $37.5122   $37.51   $37.50   $37.50  
  Purchase #2 $193.98   9.648%   $212.6952   $212.70   $212.70   $212.70  
  Purchase #3 $247.94   5.785%   $262.2833   $262.28   $262.30   $262.30  
  Purchase #4 $238.47   4.171%   $248.4166   $248.42   $248.40   $248.40  
  Purchase #5 $183.76   4.405%   $191.8546   $191.85   $191.85   $191.90  
  Purchase #6 $195.48   5.301%   $205.8424   $205.84   $205.85   $205.80  
  Purchase #7 $91.62   9.401%   $100.2332   $100.23   $100.25   $100.20  
  7 purchase totals = $1,184.83       $1,258.8375   $1,258.83   $1,258.85   $1,258.80