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 $210.80   11.801%   $235.6765   $235.68   $235.70   $235.70  
  Purchase #2 $90.26   7.828%   $97.3256   $97.33   $97.35   $97.30  
  Purchase #3 $135.40   7.638%   $145.7419   $145.74   $145.75   $145.70  
  Purchase #4 $181.91   9.177%   $198.6039   $198.60   $198.60   $198.60  
  Purchase #5 $241.38   13.353%   $273.6115   $273.61   $273.60   $273.60  
  Purchase #6 $34.28   11.181%   $38.1128   $38.11   $38.10   $38.10  
  Purchase #7 $62.53   6.507%   $66.5988   $66.60   $66.60   $66.60  
  7 purchase totals = $956.56       $1,055.6710   $1,055.67   $1,055.70   $1,055.60