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 $115.53   6.488%   $123.0256   $123.03   $123.05   $123.00  
  Purchase #2 $208.31   7.808%   $224.5748   $224.57   $224.55   $224.60  
  Purchase #3 $61.45   3.491%   $63.5952   $63.60   $63.60   $63.60  
  Purchase #4 $61.36   5.157%   $64.5243   $64.52   $64.50   $64.50  
  Purchase #5 $64.87   13.518%   $73.6391   $73.64   $73.65   $73.60  
  Purchase #6 $139.59   6.754%   $149.0179   $149.02   $149.00   $149.00  
  Purchase #7 $32.75   9.773%   $35.9507   $35.95   $35.95   $36.00  
  7 purchase totals = $683.86       $734.3276   $734.33   $734.30   $734.30