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 $170.26   8.260%   $184.3235   $184.32   $184.30   $184.30  
  Purchase #2 $143.84   3.343%   $148.6486   $148.65   $148.65   $148.60  
  Purchase #3 $23.34   5.782%   $24.6895   $24.69   $24.70   $24.70  
  Purchase #4 $247.94   8.634%   $269.3471   $269.35   $269.35   $269.30  
  Purchase #5 $165.67   9.798%   $181.9023   $181.90   $181.90   $181.90  
  Purchase #6 $33.44   3.590%   $34.6405   $34.64   $34.65   $34.60  
  Purchase #7 $208.35   11.183%   $231.6498   $231.65   $231.65   $231.60  
  7 purchase totals = $992.84       $1,075.2013   $1,075.20   $1,075.20   $1,075.00