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 $33.73   11.606%   $37.6447   $37.64   $37.65   $37.60  
  Purchase #2 $119.36   6.231%   $126.7973   $126.80   $126.80   $126.80  
  Purchase #3 $184.71   9.646%   $202.5271   $202.53   $202.55   $202.50  
  Purchase #4 $220.83   5.240%   $232.4015   $232.40   $232.40   $232.40  
  Purchase #5 $76.55   7.580%   $82.3525   $82.35   $82.35   $82.40  
  Purchase #6 $183.36   5.364%   $193.1954   $193.20   $193.20   $193.20  
  Purchase #7 $164.30   4.224%   $171.24   $171.24   $171.25   $171.20  
  7 purchase totals = $982.84       $1,046.1585   $1,046.16   $1,046.20   $1,046.10