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 $54.38   7.133%   $58.2589   $58.26   $58.25   $58.30  
  Purchase #2 $94.29   3.138%   $97.2488   $97.25   $97.25   $97.20  
  Purchase #3 $53.56   6.163%   $56.8609   $56.86   $56.85   $56.90  
  Purchase #4 $119.90   6.219%   $127.3566   $127.36   $127.35   $127.40  
  Purchase #5 $74.40   3.499%   $77.0033   $77.00   $77.00   $77.00  
  Purchase #6 $49.96   9.400%   $54.6562   $54.66   $54.65   $54.70  
  Purchase #7 $140.93   11.309%   $156.8678   $156.87   $156.85   $156.90  
  7 purchase totals = $587.42       $628.2525   $628.26   $628.20   $628.40