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 $54.59   11.146%   $60.6746   $60.67   $60.65   $60.70  
  Purchase #2 $34.59   5.822%   $36.6038   $36.60   $36.60   $36.60  
  Purchase #3 $153.74   10.628%   $170.0795   $170.08   $170.10   $170.10  
  Purchase #4 $99.63   4.318%   $103.932   $103.93   $103.95   $103.90  
  Purchase #5 $82.92   4.347%   $86.5245   $86.52   $86.50   $86.50  
  Purchase #6 $120.46   11.634%   $134.4743   $134.47   $134.45   $134.50  
  Purchase #7 $200.69   5.173%   $211.0717   $211.07   $211.05   $211.10  
  7 purchase totals = $746.62       $803.3604   $803.34   $803.30   $803.40