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 $192.62   10.426%   $212.7026   $212.70   $212.70   $212.70  
  Purchase #2 $178.94   13.215%   $202.5869   $202.59   $202.60   $202.60  
  Purchase #3 $43.61   11.136%   $48.4664   $48.47   $48.45   $48.50  
  Purchase #4 $166.95   5.484%   $176.1055   $176.11   $176.10   $176.10  
  Purchase #5 $162.30   6.163%   $172.3025   $172.30   $172.30   $172.30  
  Purchase #6 $152.62   3.832%   $158.4684   $158.47   $158.45   $158.50  
  Purchase #7 $46.72   6.690%   $49.8456   $49.85   $49.85   $49.80  
  7 purchase totals = $943.76       $1,020.4779   $1,020.49   $1,020.45   $1,020.50