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 $178.93   3.712%   $185.5719   $185.57   $185.55   $185.60  
  Purchase #2 $228.90   11.258%   $254.6696   $254.67   $254.65   $254.70  
  Purchase #3 $171.42   12.755%   $193.2846   $193.28   $193.30   $193.30  
  Purchase #4 $33.71   13.526%   $38.2696   $38.27   $38.25   $38.30  
  Purchase #5 $215.90   9.507%   $236.4256   $236.43   $236.45   $236.40  
  Purchase #6 $92.32   4.728%   $96.6849   $96.68   $96.70   $96.70  
  Purchase #7 $44.55   5.459%   $46.982   $46.98   $47.00   $47.00  
  7 purchase totals = $965.73       $1,051.8882   $1,051.88   $1,051.90   $1,052.00