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 $210.54   10.331%   $232.2909   $232.29   $232.30   $232.30  
  Purchase #2 $64.45   8.598%   $69.9914   $69.99   $70.00   $70.00  
  Purchase #3 $79.39   7.809%   $85.5896   $85.59   $85.60   $85.60  
  Purchase #4 $32.93   9.272%   $35.9833   $35.98   $36.00   $36.00  
  Purchase #5 $175.96   5.198%   $185.1064   $185.11   $185.10   $185.10  
  Purchase #6 $187.82   4.454%   $196.1855   $196.19   $196.20   $196.20  
  Purchase #7 $218.58   9.603%   $239.5702   $239.57   $239.55   $239.60  
  7 purchase totals = $969.67       $1,044.7173   $1,044.72   $1,044.75   $1,044.80