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 $228.99   10.299%   $252.5737   $252.57   $252.55   $252.60  
  Purchase #2 $24.84   4.627%   $25.9893   $25.99   $26.00   $26.00  
  Purchase #3 $31.48   3.327%   $32.5273   $32.53   $32.55   $32.50  
  Purchase #4 $122.96   5.118%   $129.2531   $129.25   $129.25   $129.30  
  Purchase #5 $97.72   7.267%   $104.8213   $104.82   $104.80   $104.80  
  Purchase #6 $71.93   3.619%   $74.5331   $74.53   $74.55   $74.50  
  Purchase #7 $164.66   4.574%   $172.1915   $172.19   $172.20   $172.20  
  7 purchase totals = $742.58       $791.8893   $791.88   $791.90   $791.90