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 $201.79   11.760%   $225.5205   $225.52   $225.50   $225.50  
  Purchase #2 $125.51   4.152%   $130.7212   $130.72   $130.70   $130.70  
  Purchase #3 $227.31   9.214%   $248.2543   $248.25   $248.25   $248.30  
  Purchase #4 $189.99   12.227%   $213.2201   $213.22   $213.20   $213.20  
  Purchase #5 $230.26   9.517%   $252.1738   $252.17   $252.15   $252.20  
  Purchase #6 $26.72   3.267%   $27.5929   $27.59   $27.60   $27.60  
  Purchase #7 $56.80   8.764%   $61.778   $61.78   $61.80   $61.80  
  7 purchase totals = $1,058.38       $1,159.2608   $1,159.25   $1,159.20   $1,159.30