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 $164.62   6.514%   $175.3433   $175.34   $175.35   $175.30  
  Purchase #2 $170.94   12.430%   $192.1878   $192.19   $192.20   $192.20  
  Purchase #3 $236.28   9.542%   $258.8258   $258.83   $258.85   $258.80  
  Purchase #4 $43.45   6.276%   $46.1769   $46.18   $46.20   $46.20  
  Purchase #5 $14.69   9.786%   $16.1276   $16.13   $16.15   $16.10  
  Purchase #6 $212.96   10.673%   $235.6892   $235.69   $235.70   $235.70  
  Purchase #7 $150.84   9.166%   $164.666   $164.67   $164.65   $164.70  
  7 purchase totals = $993.78       $1,089.0166   $1,089.03   $1,089.10   $1,089.00