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 $135.66   8.489%   $147.1762   $147.18   $147.20   $147.20  
  Purchase #2 $74.83   12.865%   $84.4569   $84.46   $84.45   $84.50  
  Purchase #3 $23.78   11.226%   $26.4495   $26.45   $26.45   $26.40  
  Purchase #4 $161.70   3.384%   $167.1719   $167.17   $167.15   $167.20  
  Purchase #5 $118.63   3.866%   $123.2162   $123.22   $123.20   $123.20  
  Purchase #6 $235.27   3.538%   $243.5939   $243.59   $243.60   $243.60  
  Purchase #7 $203.94   8.662%   $221.6053   $221.61   $221.60   $221.60  
  7 purchase totals = $953.81       $1,013.6699   $1,013.68   $1,013.65   $1,013.70