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 $68.52   13.135%   $77.5201   $77.52   $77.50   $77.50  
  Purchase #2 $176.71   12.389%   $198.6026   $198.60   $198.60   $198.60  
  Purchase #3 $214.96   3.132%   $221.6925   $221.69   $221.70   $221.70  
  Purchase #4 $110.61   11.457%   $123.2826   $123.28   $123.30   $123.30  
  Purchase #5 $205.34   3.394%   $212.3092   $212.31   $212.30   $212.30  
  Purchase #6 $240.65   9.662%   $263.9016   $263.90   $263.90   $263.90  
  Purchase #7 $166.51   11.703%   $185.9967   $186.00   $186.00   $186.00  
  7 purchase totals = $1,183.30       $1,283.3053   $1,283.30   $1,283.30   $1,283.30