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 $89.53   6.561%   $95.4041   $95.40   $95.40   $95.40  
  Purchase #2 $58.44   4.252%   $60.9249   $60.92   $60.90   $60.90  
  Purchase #3 $199.97   11.699%   $223.3645   $223.36   $223.35   $223.40  
  Purchase #4 $219.55   4.676%   $229.8162   $229.82   $229.80   $229.80  
  Purchase #5 $230.82   13.732%   $262.5162   $262.52   $262.50   $262.50  
  Purchase #6 $171.26   13.258%   $193.9657   $193.97   $193.95   $194.00  
  Purchase #7 $176.79   7.863%   $190.691   $190.69   $190.70   $190.70  
  7 purchase totals = $1,146.36       $1,256.6826   $1,256.68   $1,256.60   $1,256.70