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 $161.30   11.160%   $179.3011   $179.30   $179.30   $179.30  
  Purchase #2 $70.33   4.667%   $73.6123   $73.61   $73.60   $73.60  
  Purchase #3 $41.44   12.695%   $46.7008   $46.70   $46.70   $46.70  
  Purchase #4 $84.84   9.599%   $92.9838   $92.98   $93.00   $93.00  
  Purchase #5 $238.75   12.843%   $269.4127   $269.41   $269.40   $269.40  
  Purchase #6 $42.67   8.414%   $46.2603   $46.26   $46.25   $46.30  
  Purchase #7 $235.51   12.816%   $265.693   $265.69   $265.70   $265.70  
  7 purchase totals = $874.84       $973.9640   $973.95   $973.95   $974.00