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 $226.71   3.737%   $235.1822   $235.18   $235.20   $235.20  
  Purchase #2 $23.71   3.401%   $24.5164   $24.52   $24.50   $24.50  
  Purchase #3 $120.31   13.508%   $136.5615   $136.56   $136.55   $136.60  
  Purchase #4 $53.40   3.388%   $55.2092   $55.21   $55.20   $55.20  
  Purchase #5 $236.47   13.371%   $268.0884   $268.09   $268.10   $268.10  
  Purchase #6 $114.66   13.837%   $130.5255   $130.53   $130.55   $130.50  
  Purchase #7 $196.77   11.188%   $218.7846   $218.78   $218.80   $218.80  
  7 purchase totals = $972.03       $1,068.8678   $1,068.87   $1,068.90   $1,068.90