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 $63.66   6.848%   $68.0194   $68.02   $68.00   $68.00  
  Purchase #2 $175.88   11.126%   $195.4484   $195.45   $195.45   $195.40  
  Purchase #3 $109.80   11.646%   $122.5873   $122.59   $122.60   $122.60  
  Purchase #4 $248.39   12.369%   $279.1134   $279.11   $279.10   $279.10  
  Purchase #5 $105.52   7.301%   $113.224   $113.22   $113.20   $113.20  
  Purchase #6 $85.59   11.795%   $95.6853   $95.69   $95.70   $95.70  
  Purchase #7 $132.89   9.663%   $145.7312   $145.73   $145.75   $145.70  
  7 purchase totals = $921.73       $1,019.8090   $1,019.81   $1,019.80   $1,019.70