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 $204.88   10.741%   $226.8862   $226.89   $226.90   $226.90  
  Purchase #2 $88.63   7.288%   $95.0894   $95.09   $95.10   $95.10  
  Purchase #3 $88.32   5.732%   $93.3825   $93.38   $93.40   $93.40  
  Purchase #4 $161.85   4.424%   $169.0102   $169.01   $169.00   $169.00  
  Purchase #5 $235.43   11.580%   $262.6928   $262.69   $262.70   $262.70  
  Purchase #6 $8.59   12.141%   $9.6329   $9.63   $9.65   $9.60  
  Purchase #7 $156.99   8.153%   $169.7894   $169.79   $169.80   $169.80  
  7 purchase totals = $944.69       $1,026.4834   $1,026.48   $1,026.55   $1,026.50