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 $56.56   13.698%   $64.3076   $64.31   $64.30   $64.30  
  Purchase #2 $212.83   11.461%   $237.2224   $237.22   $237.20   $237.20  
  Purchase #3 $247.77   6.795%   $264.606   $264.61   $264.60   $264.60  
  Purchase #4 $223.78   10.824%   $248.0019   $248.00   $248.00   $248.00  
  Purchase #5 $92.66   12.276%   $104.0349   $104.03   $104.05   $104.00  
  Purchase #6 $129.78   6.307%   $137.9652   $137.97   $137.95   $138.00  
  Purchase #7 $142.61   12.257%   $160.0897   $160.09   $160.10   $160.10  
  7 purchase totals = $1,105.99       $1,216.2277   $1,216.23   $1,216.20   $1,216.20