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 $236.93   13.705%   $269.4013   $269.40   $269.40   $269.40  
  Purchase #2 $161.74   9.439%   $177.0066   $177.01   $177.00   $177.00  
  Purchase #3 $62.93   10.118%   $69.2973   $69.30   $69.30   $69.30  
  Purchase #4 $225.48   12.714%   $254.1475   $254.15   $254.15   $254.10  
  Purchase #5 $183.73   5.333%   $193.5283   $193.53   $193.55   $193.50  
  Purchase #6 $245.93   7.597%   $264.6133   $264.61   $264.60   $264.60  
  Purchase #7 $151.52   9.822%   $166.4023   $166.40   $166.40   $166.40  
  7 purchase totals = $1,268.26       $1,394.3966   $1,394.40   $1,394.40   $1,394.30