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 $239.79   12.577%   $269.9484   $269.95   $269.95   $269.90  
  Purchase #2 $71.96   5.257%   $75.7429   $75.74   $75.75   $75.70  
  Purchase #3 $34.38   12.481%   $38.671   $38.67   $38.65   $38.70  
  Purchase #4 $126.72   8.285%   $137.2188   $137.22   $137.20   $137.20  
  Purchase #5 $97.29   9.597%   $106.6269   $106.63   $106.65   $106.60  
  Purchase #6 $169.74   12.761%   $191.4005   $191.40   $191.40   $191.40  
  Purchase #7 $230.99   9.144%   $252.1117   $252.11   $252.10   $252.10  
  7 purchase totals = $970.87       $1,071.7202   $1,071.72   $1,071.70   $1,071.60