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 $241.53   8.558%   $262.2001   $262.20   $262.20   $262.20  
  Purchase #2 $18.93   7.436%   $20.3376   $20.34   $20.35   $20.30  
  Purchase #3 $57.28   11.363%   $63.7887   $63.79   $63.80   $63.80  
  Purchase #4 $55.53   9.376%   $60.7365   $60.74   $60.75   $60.70  
  Purchase #5 $187.85   9.782%   $206.2255   $206.23   $206.25   $206.20  
  Purchase #6 $158.49   3.133%   $163.4555   $163.46   $163.45   $163.50  
  Purchase #7 $31.25   11.223%   $34.7572   $34.76   $34.75   $34.80  
  7 purchase totals = $750.86       $811.5011   $811.52   $811.55   $811.50