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 $84.56   9.156%   $92.3023   $92.30   $92.30   $92.30  
  Purchase #2 $161.49   9.626%   $177.035   $177.04   $177.05   $177.00  
  Purchase #3 $151.87   13.293%   $172.0581   $172.06   $172.05   $172.10  
  Purchase #4 $208.29   12.388%   $234.093   $234.09   $234.10   $234.10  
  Purchase #5 $246.49   8.713%   $267.9667   $267.97   $267.95   $268.00  
  Purchase #6 $123.74   11.597%   $138.0901   $138.09   $138.10   $138.10  
  Purchase #7 $64.25   11.562%   $71.6786   $71.68   $71.70   $71.70  
  7 purchase totals = $1,040.69       $1,153.2238   $1,153.23   $1,153.25   $1,153.30