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 $213.51   10.113%   $235.1023   $235.10   $235.10   $235.10  
  Purchase #2 $19.93   13.641%   $22.6487   $22.65   $22.65   $22.60  
  Purchase #3 $69.93   6.851%   $74.7209   $74.72   $74.70   $74.70  
  Purchase #4 $131.72   5.583%   $139.0739   $139.07   $139.05   $139.10  
  Purchase #5 $167.82   7.788%   $180.8898   $180.89   $180.90   $180.90  
  Purchase #6 $201.31   3.514%   $208.384   $208.38   $208.40   $208.40  
  Purchase #7 $180.79   12.848%   $204.0179   $204.02   $204.00   $204.00  
  7 purchase totals = $985.01       $1,064.8375   $1,064.83   $1,064.80   $1,064.80