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 $52.43   8.380%   $56.8236   $56.82   $56.80   $56.80  
  Purchase #2 $222.82   12.155%   $249.9038   $249.90   $249.90   $249.90  
  Purchase #3 $50.54   3.297%   $52.2063   $52.21   $52.20   $52.20  
  Purchase #4 $233.81   12.131%   $262.1735   $262.17   $262.15   $262.20  
  Purchase #5 $8.89   5.793%   $9.405   $9.41   $9.40   $9.40  
  Purchase #6 $83.74   5.771%   $88.5726   $88.57   $88.55   $88.60  
  Purchase #7 $125.52   9.149%   $137.0038   $137.00   $137.00   $137.00  
  7 purchase totals = $777.75       $856.0886   $856.08   $856.00   $856.10