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 $56.86   6.587%   $60.6054   $60.61   $60.60   $60.60  
  Purchase #2 $17.96   4.839%   $18.8291   $18.83   $18.85   $18.80  
  Purchase #3 $223.62   10.761%   $247.6837   $247.68   $247.70   $247.70  
  Purchase #4 $8.60   4.803%   $9.0131   $9.01   $9.00   $9.00  
  Purchase #5 $123.41   5.586%   $130.3037   $130.30   $130.30   $130.30  
  Purchase #6 $37.66   5.857%   $39.8657   $39.87   $39.85   $39.90  
  Purchase #7 $239.52   8.733%   $260.4373   $260.44   $260.45   $260.40  
  7 purchase totals = $707.63       $766.7380   $766.74   $766.75   $766.70