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 $118.89   13.482%   $134.9187   $134.92   $134.90   $134.90  
  Purchase #2 $177.69   8.215%   $192.2872   $192.29   $192.30   $192.30  
  Purchase #3 $27.36   6.507%   $29.1403   $29.14   $29.15   $29.10  
  Purchase #4 $240.61   6.261%   $255.6746   $255.67   $255.65   $255.70  
  Purchase #5 $223.94   12.825%   $252.6603   $252.66   $252.65   $252.70  
  Purchase #6 $156.83   6.769%   $167.4458   $167.45   $167.45   $167.40  
  Purchase #7 $21.80   11.608%   $24.3305   $24.33   $24.35   $24.30  
  7 purchase totals = $967.12       $1,056.4574   $1,056.46   $1,056.45   $1,056.40