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 $161.49   13.471%   $183.2443   $183.24   $183.25   $183.20  
  Purchase #2 $233.77   9.697%   $256.4387   $256.44   $256.45   $256.40  
  Purchase #3 $50.52   7.235%   $54.1751   $54.18   $54.20   $54.20  
  Purchase #4 $207.40   11.358%   $230.9565   $230.96   $230.95   $231.00  
  Purchase #5 $135.70   7.782%   $146.2602   $146.26   $146.25   $146.30  
  Purchase #6 $165.87   11.653%   $185.1988   $185.20   $185.20   $185.20  
  Purchase #7 $182.81   7.590%   $196.6853   $196.69   $196.70   $196.70  
  7 purchase totals = $1,137.56       $1,252.9589   $1,252.97   $1,253.00   $1,253.00