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 $57.65   11.405%   $64.225   $64.23   $64.25   $64.20  
  Purchase #2 $161.77   3.572%   $167.5484   $167.55   $167.55   $167.50  
  Purchase #3 $81.95   8.650%   $89.0387   $89.04   $89.05   $89.00  
  Purchase #4 $248.91   5.275%   $262.04   $262.04   $262.05   $262.00  
  Purchase #5 $124.25   11.229%   $138.202   $138.20   $138.20   $138.20  
  Purchase #6 $210.92   11.155%   $234.4481   $234.45   $234.45   $234.40  
  Purchase #7 $9.40   13.843%   $10.7012   $10.70   $10.70   $10.70  
  7 purchase totals = $894.85       $966.2034   $966.21   $966.25   $966.00