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 $13.28   9.657%   $14.5624   $14.56   $14.55   $14.60  
  Purchase #2 $210.53   6.693%   $224.6208   $224.62   $224.60   $224.60  
  Purchase #3 $111.27   6.699%   $118.724   $118.72   $118.70   $118.70  
  Purchase #4 $193.87   8.486%   $210.3218   $210.32   $210.30   $210.30  
  Purchase #5 $190.96   11.340%   $212.6149   $212.61   $212.60   $212.60  
  Purchase #6 $171.92   4.285%   $179.2868   $179.29   $179.30   $179.30  
  Purchase #7 $88.41   9.177%   $96.5234   $96.52   $96.50   $96.50  
  7 purchase totals = $980.24       $1,056.6541   $1,056.64   $1,056.55   $1,056.60