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 $142.85   8.273%   $154.668   $154.67   $154.65   $154.70  
  Purchase #2 $41.46   8.217%   $44.8668   $44.87   $44.85   $44.90  
  Purchase #3 $187.69   7.293%   $201.3782   $201.38   $201.40   $201.40  
  Purchase #4 $106.66   12.405%   $119.8912   $119.89   $119.90   $119.90  
  Purchase #5 $223.88   12.743%   $252.409   $252.41   $252.40   $252.40  
  Purchase #6 $170.80   3.217%   $176.2946   $176.29   $176.30   $176.30  
  Purchase #7 $62.55   10.284%   $68.9826   $68.98   $69.00   $69.00  
  7 purchase totals = $935.89       $1,018.4904   $1,018.49   $1,018.50   $1,018.60