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 $69.65   4.297%   $72.6429   $72.64   $72.65   $72.60  
  Purchase #2 $147.81   3.340%   $152.7469   $152.75   $152.75   $152.70  
  Purchase #3 $139.74   6.352%   $148.6163   $148.62   $148.60   $148.60  
  Purchase #4 $89.27   7.252%   $95.7439   $95.74   $95.75   $95.70  
  Purchase #5 $52.76   8.730%   $57.3659   $57.37   $57.35   $57.40  
  Purchase #6 $246.57   6.682%   $263.0458   $263.05   $263.05   $263.00  
  Purchase #7 $12.52   5.352%   $13.1901   $13.19   $13.20   $13.20  
  7 purchase totals = $758.32       $803.3518   $803.36   $803.35   $803.20