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 $82.43   7.783%   $88.8455   $88.85   $88.85   $88.80  
  Purchase #2 $134.74   8.294%   $145.9153   $145.92   $145.90   $145.90  
  Purchase #3 $187.70   11.724%   $209.7059   $209.71   $209.70   $209.70  
  Purchase #4 $84.57   7.122%   $90.5931   $90.59   $90.60   $90.60  
  Purchase #5 $222.66   8.866%   $242.401   $242.40   $242.40   $242.40  
  Purchase #6 $80.81   7.150%   $86.5879   $86.59   $86.60   $86.60  
  Purchase #7 $36.51   12.352%   $41.0197   $41.02   $41.00   $41.00  
  7 purchase totals = $829.42       $905.0684   $905.08   $905.05   $905.00