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 $25.52   4.143%   $26.5773   $26.58   $26.60   $26.60  
  Purchase #2 $196.94   11.218%   $219.0327   $219.03   $219.05   $219.00  
  Purchase #3 $109.35   6.683%   $116.6579   $116.66   $116.65   $116.70  
  Purchase #4 $114.34   5.345%   $120.4515   $120.45   $120.45   $120.50  
  Purchase #5 $211.69   11.566%   $236.1741   $236.17   $236.15   $236.20  
  Purchase #6 $130.85   4.343%   $136.5328   $136.53   $136.55   $136.50  
  Purchase #7 $61.36   11.645%   $68.5054   $68.51   $68.50   $68.50  
  7 purchase totals = $850.05       $923.9317   $923.93   $923.95   $924.00