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 $202.44   3.106%   $208.7278   $208.73   $208.75   $208.70  
  Purchase #2 $73.49   6.845%   $78.5204   $78.52   $78.50   $78.50  
  Purchase #3 $181.77   6.270%   $193.167   $193.17   $193.15   $193.20  
  Purchase #4 $101.48   7.690%   $109.2838   $109.28   $109.30   $109.30  
  Purchase #5 $154.60   4.131%   $160.9865   $160.99   $161.00   $161.00  
  Purchase #6 $99.45   3.691%   $103.1207   $103.12   $103.10   $103.10  
  Purchase #7 $181.80   6.779%   $194.1242   $194.12   $194.10   $194.10  
  7 purchase totals = $995.03       $1,047.9304   $1,047.93   $1,047.90   $1,047.90