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 $58.80   11.385%   $65.4944   $65.49   $65.50   $65.50  
  Purchase #2 $235.87   12.764%   $265.9764   $265.98   $266.00   $266.00  
  Purchase #3 $164.65   6.245%   $174.9324   $174.93   $174.95   $174.90  
  Purchase #4 $9.83   13.186%   $11.1262   $11.13   $11.15   $11.10  
  Purchase #5 $82.45   11.556%   $91.9779   $91.98   $92.00   $92.00  
  Purchase #6 $113.26   13.332%   $128.3598   $128.36   $128.35   $128.40  
  Purchase #7 $43.68   12.870%   $49.3016   $49.30   $49.30   $49.30  
  7 purchase totals = $708.54       $787.1687   $787.17   $787.25   $787.20