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 $224.67   6.298%   $238.8197   $238.82   $238.80   $238.80  
  Purchase #2 $41.82   10.613%   $46.2584   $46.26   $46.25   $46.30  
  Purchase #3 $98.67   9.381%   $107.9262   $107.93   $107.95   $107.90  
  Purchase #4 $218.31   6.843%   $233.249   $233.25   $233.25   $233.20  
  Purchase #5 $219.52   4.780%   $230.0131   $230.01   $230.00   $230.00  
  Purchase #6 $179.71   7.610%   $193.3859   $193.39   $193.40   $193.40  
  Purchase #7 $188.60   4.234%   $196.5853   $196.59   $196.60   $196.60  
  7 purchase totals = $1,171.30       $1,246.2376   $1,246.25   $1,246.25   $1,246.20