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 $211.58   6.692%   $225.7389   $225.74   $225.75   $225.70  
  Purchase #2 $149.77   11.418%   $166.8707   $166.87   $166.85   $166.90  
  Purchase #3 $239.81   13.272%   $271.6376   $271.64   $271.65   $271.60  
  Purchase #4 $237.26   3.350%   $245.2082   $245.21   $245.20   $245.20  
  Purchase #5 $186.30   8.260%   $201.6884   $201.69   $201.70   $201.70  
  Purchase #6 $222.28   5.862%   $235.3101   $235.31   $235.30   $235.30  
  Purchase #7 $122.98   3.286%   $127.0211   $127.02   $127.00   $127.00  
  7 purchase totals = $1,369.98       $1,473.4750   $1,473.48   $1,473.45   $1,473.40