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 $147.43   13.722%   $167.6603   $167.66   $167.65   $167.70  
  Purchase #2 $224.70   13.187%   $254.3312   $254.33   $254.35   $254.30  
  Purchase #3 $23.58   4.501%   $24.6413   $24.64   $24.65   $24.60  
  Purchase #4 $236.67   11.154%   $263.0682   $263.07   $263.05   $263.10  
  Purchase #5 $155.43   11.659%   $173.5516   $173.55   $173.55   $173.60  
  Purchase #6 $81.36   11.292%   $90.5472   $90.55   $90.55   $90.50  
  Purchase #7 $219.91   5.687%   $232.4163   $232.42   $232.40   $232.40  
  7 purchase totals = $1,089.08       $1,206.2161   $1,206.22   $1,206.20   $1,206.20