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 $125.31   7.295%   $134.4514   $134.45   $134.45   $134.50  
  Purchase #2 $38.89   6.109%   $41.2658   $41.27   $41.25   $41.30  
  Purchase #3 $77.40   13.104%   $87.5425   $87.54   $87.55   $87.50  
  Purchase #4 $67.55   13.470%   $76.649   $76.65   $76.65   $76.60  
  Purchase #5 $167.48   5.488%   $176.6713   $176.67   $176.65   $176.70  
  Purchase #6 $195.93   6.841%   $209.3336   $209.33   $209.35   $209.30  
  Purchase #7 $226.50   5.792%   $239.6189   $239.62   $239.60   $239.60  
  7 purchase totals = $899.06       $965.5325   $965.53   $965.50   $965.50