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 $162.67   13.549%   $184.7102   $184.71   $184.70   $184.70  
  Purchase #2 $201.55   9.316%   $220.3264   $220.33   $220.35   $220.30  
  Purchase #3 $65.25   6.163%   $69.2714   $69.27   $69.25   $69.30  
  Purchase #4 $181.70   11.238%   $202.1194   $202.12   $202.10   $202.10  
  Purchase #5 $202.69   9.594%   $222.1361   $222.14   $222.15   $222.10  
  Purchase #6 $15.67   12.544%   $17.6356   $17.64   $17.65   $17.60  
  Purchase #7 $158.75   3.636%   $164.5222   $164.52   $164.50   $164.50  
  7 purchase totals = $988.28       $1,080.7213   $1,080.73   $1,080.70   $1,080.60