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 $218.93   11.124%   $243.2838   $243.28   $243.30   $243.30  
  Purchase #2 $192.51   8.545%   $208.96   $208.96   $208.95   $209.00  
  Purchase #3 $32.27   5.472%   $34.0358   $34.04   $34.05   $34.00  
  Purchase #4 $196.32   4.711%   $205.5686   $205.57   $205.55   $205.60  
  Purchase #5 $87.45   8.144%   $94.5719   $94.57   $94.55   $94.60  
  Purchase #6 $150.97   5.333%   $159.0212   $159.02   $159.00   $159.00  
  Purchase #7 $6.76   4.706%   $7.0781   $7.08   $7.10   $7.10  
  7 purchase totals = $885.21       $952.5194   $952.52   $952.50   $952.60