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 $59.66   9.718%   $65.4578   $65.46   $65.45   $65.50  
  Purchase #2 $174.54   6.150%   $185.2742   $185.27   $185.25   $185.30  
  Purchase #3 $217.64   11.772%   $243.2606   $243.26   $243.25   $243.30  
  Purchase #4 $180.56   12.870%   $203.7981   $203.80   $203.80   $203.80  
  Purchase #5 $95.30   13.406%   $108.0759   $108.08   $108.10   $108.10  
  Purchase #6 $231.84   6.274%   $246.3856   $246.39   $246.40   $246.40  
  Purchase #7 $176.60   3.764%   $183.2472   $183.25   $183.25   $183.20  
  7 purchase totals = $1,136.14       $1,235.4994   $1,235.51   $1,235.50   $1,235.60