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 $223.61   12.423%   $251.3891   $251.39   $251.40   $251.40  
  Purchase #2 $92.96   5.596%   $98.162   $98.16   $98.15   $98.20  
  Purchase #3 $177.64   12.461%   $199.7757   $199.78   $199.80   $199.80  
  Purchase #4 $219.54   6.826%   $234.5258   $234.53   $234.55   $234.50  
  Purchase #5 $84.89   8.737%   $92.3068   $92.31   $92.30   $92.30  
  Purchase #6 $211.31   11.179%   $234.9323   $234.93   $234.95   $234.90  
  Purchase #7 $169.94   12.748%   $191.604   $191.60   $191.60   $191.60  
  7 purchase totals = $1,179.89       $1,302.6957   $1,302.70   $1,302.75   $1,302.70