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 $31.33   12.614%   $35.282   $35.28   $35.30   $35.30  
  Purchase #2 $84.53   10.691%   $93.5671   $93.57   $93.55   $93.60  
  Purchase #3 $172.79   10.238%   $190.4802   $190.48   $190.50   $190.50  
  Purchase #4 $189.40   6.640%   $201.9762   $201.98   $202.00   $202.00  
  Purchase #5 $115.95   5.671%   $122.5255   $122.53   $122.55   $122.50  
  Purchase #6 $186.95   11.746%   $208.9091   $208.91   $208.90   $208.90  
  Purchase #7 $82.34   12.437%   $92.5806   $92.58   $92.60   $92.60  
  7 purchase totals = $863.29       $945.3207   $945.33   $945.40   $945.40