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 $105.35   7.764%   $113.5294   $113.53   $113.55   $113.50  
  Purchase #2 $211.32   9.281%   $230.9326   $230.93   $230.95   $230.90  
  Purchase #3 $64.50   6.329%   $68.5822   $68.58   $68.60   $68.60  
  Purchase #4 $82.41   11.626%   $91.991   $91.99   $92.00   $92.00  
  Purchase #5 $166.44   12.530%   $187.2949   $187.29   $187.30   $187.30  
  Purchase #6 $186.35   11.833%   $208.4008   $208.40   $208.40   $208.40  
  Purchase #7 $87.35   9.769%   $95.8832   $95.88   $95.90   $95.90  
  7 purchase totals = $903.72       $996.6141   $996.60   $996.70   $996.60