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 $192.65   6.788%   $205.7271   $205.73   $205.75   $205.70  
  Purchase #2 $156.73   11.166%   $174.2305   $174.23   $174.25   $174.20  
  Purchase #3 $218.85   11.708%   $244.473   $244.47   $244.45   $244.50  
  Purchase #4 $240.84   10.519%   $266.174   $266.17   $266.15   $266.20  
  Purchase #5 $157.39   10.356%   $173.6893   $173.69   $173.70   $173.70  
  Purchase #6 $243.89   3.306%   $251.953   $251.95   $251.95   $252.00  
  Purchase #7 $31.59   5.468%   $33.3173   $33.32   $33.30   $33.30  
  7 purchase totals = $1,241.94       $1,349.5642   $1,349.56   $1,349.55   $1,349.60