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 $229.83   11.500%   $256.2605   $256.26   $256.25   $256.30  
  Purchase #2 $200.58   12.225%   $225.1009   $225.10   $225.10   $225.10  
  Purchase #3 $160.52   9.148%   $175.2044   $175.20   $175.20   $175.20  
  Purchase #4 $22.80   5.289%   $24.0059   $24.01   $24.00   $24.00  
  Purchase #5 $7.33   10.223%   $8.0793   $8.08   $8.10   $8.10  
  Purchase #6 $40.45   10.516%   $44.7037   $44.70   $44.70   $44.70  
  Purchase #7 $185.79   3.104%   $191.5569   $191.56   $191.55   $191.60  
  7 purchase totals = $847.30       $924.9116   $924.91   $924.90   $925.00