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 $177.50   13.668%   $201.7607   $201.76   $201.75   $201.80  
  Purchase #2 $109.34   9.419%   $119.6387   $119.64   $119.65   $119.60  
  Purchase #3 $91.97   6.209%   $97.6804   $97.68   $97.70   $97.70  
  Purchase #4 $10.48   4.813%   $10.9844   $10.98   $11.00   $11.00  
  Purchase #5 $8.76   5.773%   $9.2657   $9.27   $9.25   $9.30  
  Purchase #6 $8.51   6.707%   $9.0808   $9.08   $9.10   $9.10  
  Purchase #7 $55.70   11.492%   $62.101   $62.10   $62.10   $62.10  
  7 purchase totals = $462.26       $510.5117   $510.51   $510.55   $510.60