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 $174.52   6.737%   $186.2774   $186.28   $186.30   $186.30  
  Purchase #2 $92.96   4.353%   $97.0065   $97.01   $97.00   $97.00  
  Purchase #3 $164.73   6.246%   $175.019   $175.02   $175.00   $175.00  
  Purchase #4 $43.51   11.349%   $48.4479   $48.45   $48.45   $48.40  
  Purchase #5 $196.48   8.393%   $212.9706   $212.97   $212.95   $213.00  
  Purchase #6 $231.66   11.634%   $258.6113   $258.61   $258.60   $258.60  
  Purchase #7 $32.25   4.442%   $33.6825   $33.68   $33.70   $33.70  
  7 purchase totals = $936.11       $1,012.0152   $1,012.02   $1,012.00   $1,012.00