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 $246.64   3.253%   $254.6632   $254.66   $254.65   $254.70  
  Purchase #2 $43.75   4.491%   $45.7148   $45.71   $45.70   $45.70  
  Purchase #3 $174.40   3.690%   $180.8354   $180.84   $180.85   $180.80  
  Purchase #4 $75.58   11.813%   $84.5083   $84.51   $84.50   $84.50  
  Purchase #5 $247.54   3.124%   $255.2731   $255.27   $255.25   $255.30  
  Purchase #6 $73.37   13.107%   $82.9866   $82.99   $83.00   $83.00  
  Purchase #7 $145.33   7.225%   $155.8301   $155.83   $155.85   $155.80  
  7 purchase totals = $1,006.61       $1,059.8115   $1,059.81   $1,059.80   $1,059.80