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 $228.44   10.414%   $252.2297   $252.23   $252.25   $252.20  
  Purchase #2 $67.33   12.267%   $75.5894   $75.59   $75.60   $75.60  
  Purchase #3 $78.93   10.830%   $87.4781   $87.48   $87.50   $87.50  
  Purchase #4 $213.26   12.800%   $240.5573   $240.56   $240.55   $240.60  
  Purchase #5 $177.70   12.781%   $200.4118   $200.41   $200.40   $200.40  
  Purchase #6 $178.66   5.376%   $188.2648   $188.26   $188.25   $188.30  
  Purchase #7 $52.90   12.519%   $59.5226   $59.52   $59.50   $59.50  
  7 purchase totals = $997.22       $1,104.0537   $1,104.05   $1,104.05   $1,104.10