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 $130.43   13.270%   $147.7381   $147.74   $147.75   $147.70  
  Purchase #2 $247.94   3.815%   $257.3989   $257.40   $257.40   $257.40  
  Purchase #3 $217.26   3.197%   $224.2058   $224.21   $224.20   $224.20  
  Purchase #4 $180.95   7.445%   $194.4217   $194.42   $194.40   $194.40  
  Purchase #5 $26.93   6.184%   $28.5954   $28.60   $28.60   $28.60  
  Purchase #6 $131.44   6.851%   $140.445   $140.45   $140.45   $140.40  
  Purchase #7 $28.41   8.512%   $30.8283   $30.83   $30.85   $30.80  
  7 purchase totals = $963.36       $1,023.6332   $1,023.65   $1,023.65   $1,023.50