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 $203.26   10.244%   $224.082   $224.08   $224.10   $224.10  
  Purchase #2 $56.67   9.593%   $62.1064   $62.11   $62.10   $62.10  
  Purchase #3 $88.53   5.621%   $93.5063   $93.51   $93.50   $93.50  
  Purchase #4 $192.34   13.561%   $218.4232   $218.42   $218.40   $218.40  
  Purchase #5 $175.52   3.468%   $181.607   $181.61   $181.60   $181.60  
  Purchase #6 $39.99   8.338%   $43.3244   $43.32   $43.30   $43.30  
  Purchase #7 $196.61   4.175%   $204.8185   $204.82   $204.80   $204.80  
  7 purchase totals = $952.92       $1,027.8678   $1,027.87   $1,027.80   $1,027.80