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 $56.73   5.145%   $59.6488   $59.65   $59.65   $59.60  
  Purchase #2 $124.46   8.467%   $134.998   $135.00   $135.00   $135.00  
  Purchase #3 $11.38   5.469%   $12.0024   $12.00   $12.00   $12.00  
  Purchase #4 $197.36   5.664%   $208.5385   $208.54   $208.55   $208.50  
  Purchase #5 $96.74   5.771%   $102.3229   $102.32   $102.30   $102.30  
  Purchase #6 $62.80   11.588%   $70.0773   $70.08   $70.10   $70.10  
  Purchase #7 $137.35   5.802%   $145.319   $145.32   $145.30   $145.30  
  7 purchase totals = $686.82       $732.9069   $732.91   $732.90   $732.80