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 $70.86   8.811%   $77.1035   $77.10   $77.10   $77.10  
  Purchase #2 $154.68   6.250%   $164.3475   $164.35   $164.35   $164.30  
  Purchase #3 $174.42   5.581%   $184.1544   $184.15   $184.15   $184.20  
  Purchase #4 $161.78   6.671%   $172.5723   $172.57   $172.55   $172.60  
  Purchase #5 $178.65   3.292%   $184.5312   $184.53   $184.55   $184.50  
  Purchase #6 $213.77   13.480%   $242.5862   $242.59   $242.60   $242.60  
  Purchase #7 $23.77   5.326%   $25.036   $25.04   $25.05   $25.00  
  7 purchase totals = $977.93       $1,050.3311   $1,050.33   $1,050.35   $1,050.30