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 $65.26   12.139%   $73.1819   $73.18   $73.20   $73.20  
  Purchase #2 $7.42   11.789%   $8.2947   $8.29   $8.30   $8.30  
  Purchase #3 $65.79   9.471%   $72.021   $72.02   $72.00   $72.00  
  Purchase #4 $121.92   12.824%   $137.555   $137.56   $137.55   $137.60  
  Purchase #5 $56.54   9.205%   $61.7445   $61.74   $61.75   $61.70  
  Purchase #6 $193.57   11.353%   $215.546   $215.55   $215.55   $215.50  
  Purchase #7 $187.63   10.498%   $207.3274   $207.33   $207.35   $207.30  
  7 purchase totals = $698.13       $775.6705   $775.67   $775.70   $775.60