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 $46.50   13.128%   $52.6045   $52.60   $52.60   $52.60  
  Purchase #2 $205.71   6.604%   $219.2951   $219.30   $219.30   $219.30  
  Purchase #3 $107.34   5.335%   $113.0666   $113.07   $113.05   $113.10  
  Purchase #4 $168.65   4.587%   $176.386   $176.39   $176.40   $176.40  
  Purchase #5 $113.69   8.678%   $123.556   $123.56   $123.55   $123.60  
  Purchase #6 $145.91   7.693%   $157.1349   $157.13   $157.15   $157.10  
  Purchase #7 $128.80   4.164%   $134.1632   $134.16   $134.15   $134.20  
  7 purchase totals = $916.60       $976.2063   $976.21   $976.20   $976.30