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 $249.62   10.554%   $275.9649   $275.96   $275.95   $276.00  
  Purchase #2 $82.91   5.523%   $87.4891   $87.49   $87.50   $87.50  
  Purchase #3 $103.36   3.741%   $107.2267   $107.23   $107.25   $107.20  
  Purchase #4 $229.45   11.716%   $256.3324   $256.33   $256.35   $256.30  
  Purchase #5 $122.79   3.134%   $126.6382   $126.64   $126.65   $126.60  
  Purchase #6 $92.79   13.370%   $105.196   $105.20   $105.20   $105.20  
  Purchase #7 $65.55   3.787%   $68.0324   $68.03   $68.05   $68.00  
  7 purchase totals = $946.47       $1,026.8797   $1,026.88   $1,026.95   $1,026.80