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 $38.45   13.470%   $43.6292   $43.63   $43.65   $43.60  
  Purchase #2 $126.73   5.473%   $133.6659   $133.67   $133.65   $133.70  
  Purchase #3 $168.55   10.821%   $186.7888   $186.79   $186.80   $186.80  
  Purchase #4 $86.58   7.462%   $93.0406   $93.04   $93.05   $93.00  
  Purchase #5 $217.52   4.170%   $226.5906   $226.59   $226.60   $226.60  
  Purchase #6 $212.34   9.218%   $231.9135   $231.91   $231.90   $231.90  
  Purchase #7 $88.75   9.516%   $97.1955   $97.20   $97.20   $97.20  
  7 purchase totals = $938.92       $1,012.8241   $1,012.83   $1,012.85   $1,012.80