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 $205.26   10.441%   $226.6912   $226.69   $226.70   $226.70  
  Purchase #2 $15.57   4.744%   $16.3086   $16.31   $16.30   $16.30  
  Purchase #3 $243.95   12.205%   $273.7241   $273.72   $273.70   $273.70  
  Purchase #4 $175.95   6.817%   $187.9445   $187.94   $187.95   $187.90  
  Purchase #5 $10.82   3.846%   $11.2361   $11.24   $11.25   $11.20  
  Purchase #6 $118.64   6.547%   $126.4074   $126.41   $126.40   $126.40  
  Purchase #7 $151.85   7.694%   $163.5333   $163.53   $163.55   $163.50  
  7 purchase totals = $922.04       $1,005.8452   $1,005.84   $1,005.85   $1,005.70