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 $203.73   3.661%   $211.1886   $211.19   $211.20   $211.20  
  Purchase #2 $67.93   5.770%   $71.8496   $71.85   $71.85   $71.80  
  Purchase #3 $53.52   4.857%   $56.1195   $56.12   $56.10   $56.10  
  Purchase #4 $161.57   11.634%   $180.3671   $180.37   $180.35   $180.40  
  Purchase #5 $33.91   13.868%   $38.6126   $38.61   $38.60   $38.60  
  Purchase #6 $135.51   10.345%   $149.5285   $149.53   $149.55   $149.50  
  Purchase #7 $161.69   10.455%   $178.5947   $178.59   $178.60   $178.60  
  7 purchase totals = $817.86       $886.2606   $886.26   $886.25   $886.20