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 $43.65   13.614%   $49.5925   $49.59   $49.60   $49.60  
  Purchase #2 $245.84   8.804%   $267.4838   $267.48   $267.50   $267.50  
  Purchase #3 $55.35   5.294%   $58.2802   $58.28   $58.30   $58.30  
  Purchase #4 $169.49   5.514%   $178.8357   $178.84   $178.85   $178.80  
  Purchase #5 $163.70   13.562%   $185.901   $185.90   $185.90   $185.90  
  Purchase #6 $71.97   4.133%   $74.9445   $74.94   $74.95   $74.90  
  Purchase #7 $193.99   4.573%   $202.8612   $202.86   $202.85   $202.90  
  7 purchase totals = $943.99       $1,017.8989   $1,017.89   $1,017.95   $1,017.90