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 $235.51   9.380%   $257.6008   $257.60   $257.60   $257.60  
  Purchase #2 $106.83   13.344%   $121.0854   $121.09   $121.10   $121.10  
  Purchase #3 $61.25   12.471%   $68.8885   $68.89   $68.90   $68.90  
  Purchase #4 $244.53   3.865%   $253.9811   $253.98   $254.00   $254.00  
  Purchase #5 $31.38   10.768%   $34.759   $34.76   $34.75   $34.80  
  Purchase #6 $202.66   4.605%   $211.9925   $211.99   $212.00   $212.00  
  Purchase #7 $203.73   12.111%   $228.4037   $228.40   $228.40   $228.40  
  7 purchase totals = $1,085.89       $1,176.7110   $1,176.71   $1,176.75   $1,176.80