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 $114.65   9.487%   $125.5268   $125.53   $125.55   $125.50  
  Purchase #2 $232.40   13.613%   $264.0366   $264.04   $264.05   $264.00  
  Purchase #3 $6.96   9.832%   $7.6443   $7.64   $7.65   $7.60  
  Purchase #4 $18.35   6.138%   $19.4763   $19.48   $19.50   $19.50  
  Purchase #5 $223.27   5.447%   $235.4315   $235.43   $235.45   $235.40  
  Purchase #6 $165.59   11.394%   $184.4573   $184.46   $184.45   $184.50  
  Purchase #7 $177.25   8.433%   $192.1975   $192.20   $192.20   $192.20  
  7 purchase totals = $938.47       $1,028.7703   $1,028.78   $1,028.85   $1,028.70