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 $200.66   11.393%   $223.5212   $223.52   $223.50   $223.50  
  Purchase #2 $151.59   6.481%   $161.4145   $161.41   $161.40   $161.40  
  Purchase #3 $240.52   8.427%   $260.7886   $260.79   $260.80   $260.80  
  Purchase #4 $32.76   3.873%   $34.0288   $34.03   $34.05   $34.00  
  Purchase #5 $112.50   3.619%   $116.5714   $116.57   $116.55   $116.60  
  Purchase #6 $157.52   3.234%   $162.6142   $162.61   $162.60   $162.60  
  Purchase #7 $47.64   11.258%   $53.0033   $53.00   $53.00   $53.00  
  7 purchase totals = $943.19       $1,011.9420   $1,011.93   $1,011.90   $1,011.90