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 $156.69   6.593%   $167.0206   $167.02   $167.00   $167.00  
  Purchase #2 $66.74   12.384%   $75.0051   $75.01   $75.00   $75.00  
  Purchase #3 $191.98   8.131%   $207.5899   $207.59   $207.60   $207.60  
  Purchase #4 $135.84   12.606%   $152.964   $152.96   $152.95   $153.00  
  Purchase #5 $239.36   10.479%   $264.4425   $264.44   $264.45   $264.40  
  Purchase #6 $211.41   8.436%   $229.2445   $229.24   $229.25   $229.20  
  Purchase #7 $36.50   9.502%   $39.9682   $39.97   $39.95   $40.00  
  7 purchase totals = $1,038.52       $1,136.2348   $1,136.23   $1,136.20   $1,136.20