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 $48.73   10.293%   $53.7458   $53.75   $53.75   $53.70  
  Purchase #2 $143.87   10.632%   $159.1663   $159.17   $159.15   $159.20  
  Purchase #3 $211.96   7.701%   $228.283   $228.28   $228.30   $228.30  
  Purchase #4 $250.54   11.743%   $279.9609   $279.96   $279.95   $280.00  
  Purchase #5 $97.69   9.529%   $106.9989   $107.00   $107.00   $107.00  
  Purchase #6 $217.43   12.728%   $245.1045   $245.10   $245.10   $245.10  
  Purchase #7 $234.99   7.649%   $252.9644   $252.96   $252.95   $253.00  
  7 purchase totals = $1,205.21       $1,326.2238   $1,326.22   $1,326.20   $1,326.30