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 $202.30   11.764%   $226.0986   $226.10   $226.10   $226.10  
  Purchase #2 $103.49   4.294%   $107.9339   $107.93   $107.95   $107.90  
  Purchase #3 $51.62   13.763%   $58.7245   $58.72   $58.70   $58.70  
  Purchase #4 $237.39   6.786%   $253.4993   $253.50   $253.50   $253.50  
  Purchase #5 $41.71   6.236%   $44.311   $44.31   $44.30   $44.30  
  Purchase #6 $97.39   8.370%   $105.5415   $105.54   $105.55   $105.50  
  Purchase #7 $236.66   11.468%   $263.8002   $263.80   $263.80   $263.80  
  7 purchase totals = $970.56       $1,059.9090   $1,059.90   $1,059.90   $1,059.80