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 $77.49   9.269%   $84.6725   $84.67   $84.65   $84.70  
  Purchase #2 $242.29   4.283%   $252.6673   $252.67   $252.65   $252.70  
  Purchase #3 $84.43   9.667%   $92.5918   $92.59   $92.60   $92.60  
  Purchase #4 $21.37   12.645%   $24.0722   $24.07   $24.05   $24.10  
  Purchase #5 $219.67   4.608%   $229.7924   $229.79   $229.80   $229.80  
  Purchase #6 $159.92   8.653%   $173.7579   $173.76   $173.75   $173.80  
  Purchase #7 $190.29   3.627%   $197.1918   $197.19   $197.20   $197.20  
  7 purchase totals = $995.46       $1,054.7459   $1,054.74   $1,054.70   $1,054.90