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 $149.96   11.726%   $167.5443   $167.54   $167.55   $167.50  
  Purchase #2 $250.61   11.565%   $279.593   $279.59   $279.60   $279.60  
  Purchase #3 $133.51   10.809%   $147.9411   $147.94   $147.95   $147.90  
  Purchase #4 $30.52   11.622%   $34.067   $34.07   $34.05   $34.10  
  Purchase #5 $226.29   12.682%   $254.9881   $254.99   $255.00   $255.00  
  Purchase #6 $35.57   3.787%   $36.917   $36.92   $36.90   $36.90  
  Purchase #7 $89.79   12.673%   $101.1691   $101.17   $101.15   $101.20  
  7 purchase totals = $916.25       $1,022.2196   $1,022.22   $1,022.20   $1,022.20